GCC has various special options that are used for debugging either your program or GCC:
-gOn most systems that use stabs format, -g enables use of extra debugging information that only GDB can use; this extra information makes debugging work better in GDB but probably makes other debuggers crash or refuse to read the program. If you want to control for certain whether to generate the extra information, use -gstabs+, -gstabs, -gxcoff+, -gxcoff, or -gvms (see below).
GCC allows you to use -g with -O. The shortcuts taken by optimized code may occasionally produce surprising results: some variables you declared may not exist at all; flow of control may briefly move where you did not expect it; some statements may not be executed because they compute constant results or their values are already at hand; some statements may execute in different places because they have been moved out of loops.
Nevertheless it proves possible to debug optimized output. This makes it reasonable to use the optimizer for programs that might have bugs.
The following options are useful when GCC is generated with the capability for more than one debugging format.
-gsplit-dwarf-ggdb-gpubnames-ggnu-pubnames-gstabs-feliminate-unused-debug-symbols-femit-class-debug-always-fdebug-types-section.debug_types section instead of making them part of the .debug_info section. It is more efficient to put them in a separate comdat sections since the linker can then remove duplicates. But not all DWARF consumers support .debug_types sections yet and on some objects .debug_types produces larger instead of smaller debugging information. -gstabs+-gcoff-gxcoff-gxcoff+-gdwarf-version
Note that with DWARF Version 2, some ports require and always use some non-conflicting DWARF 3 extensions in the unwind tables.
Version 4 may require GDB 7.0 and -fvar-tracking-assignments for maximum benefit.
-grecord-gcc-switches-frecord-gcc-switches for another way of storing compiler options into the object file. This is the default. -gno-record-gcc-switches-gstrict-dwarf-gno-strict-dwarf-gvms-glevel-ggdblevel-gstabslevel-gcofflevel-gxcofflevel-gvmslevel
Level 0 produces no debug information at all. Thus, -g0 negates -g.
Level 1 produces minimal information, enough for making backtraces in parts of the program that you don't plan to debug. This includes descriptions of functions and external variables, and line number tables, but no information about local variables.
Level 3 includes extra information, such as all the macro definitions present in the program. Some debuggers support macro expansion when you use -g3.
-gdwarf-2 does not accept a concatenated debug level, because GCC used to support an option -gdwarf that meant to generate debug information in version 1 of the DWARF format (which is very different from version 2), and it would have been too confusing. That debug format is long obsolete, but the option cannot be changed now. Instead use an additional -glevel option to change the debug level for DWARF.
-gtoggle-fcompare-debug. -fsanitize=addressASAN_OPTIONS environment variable; see https://code.google.com/p/address-sanitizer/wiki/Flags#Run-time_flags for a list of supported options. -fsanitize=kernel-address-fsanitize=threadTSAN_OPTIONS environment variable; see https://code.google.com/p/thread-sanitizer/wiki/Flags for a list of supported options. -fsanitize=leak-fsanitize=address nor -fsanitize=thread is used. In that case it will link the executable against a library that overrides malloc and other allocator functions. See https://code.google.com/p/address-sanitizer/wiki/LeakSanitizer for more details. The run-time behavior can be influenced using the LSAN_OPTIONS environment variable. -fsanitize=undefined-fsanitize=shift-fsanitize=integer-divide-by-zeroINT_MIN / -1 division. -fsanitize=unreachable__builtin_unreachable call into a diagnostics message call instead. When reaching the __builtin_unreachable call, the behavior is undefined. -fsanitize=vla-bound-std=c++1y mode, as the standard requires the exception be thrown instead. -fsanitize=null-fsanitize=return-fsanitize=signed-integer-overflow+, *, and both unary and binary - does not overflow in the signed arithmetics. Note, integer promotion rules must be taken into account. That is, the following is not an overflow: signed char a = SCHAR_MAX; a++;
While -ftrapv causes traps for signed overflows to be emitted, -fsanitize=undefined gives a diagnostic message. This currently works only for the C family of languages.
-fdump-final-insns[=file]
.), the name of the dump file is determined by appending .gkd to the compilation output file name. -fcompare-debug[=opts]
-fcompare-debug-second to the arguments passed to the second compilation. Dump the final internal representation in both compilations, and print an error if they differ. If the equal sign is omitted, the default -gtoggle is used.
The environment variable GCC_COMPARE_DEBUG, if defined, non-empty and nonzero, implicitly enables -fcompare-debug. If GCC_COMPARE_DEBUG is defined to a string starting with a dash, then it is used for opts, otherwise the default -gtoggle is used.
-fcompare-debug=, with the equal sign but without opts, is equivalent to -fno-compare-debug, which disables the dumping of the final representation and the second compilation, preventing even GCC_COMPARE_DEBUG from taking effect.
To verify full coverage during -fcompare-debug testing, set GCC_COMPARE_DEBUG to say ‘-fcompare-debug-not-overridden’, which GCC rejects as an invalid option in any actual compilation (rather than preprocessing, assembly or linking). To get just a warning, setting GCC_COMPARE_DEBUG to ‘-w%n-fcompare-debug not overridden’ will do.
-fcompare-debug-second-fcompare-debug, along with options to silence warnings, and omitting other options that would cause side-effect compiler outputs to files or to the standard output. Dump files and preserved temporary files are renamed so as to contain the .gk additional extension during the second compilation, to avoid overwriting those generated by the first. When this option is passed to the compiler driver, it causes the first compilation to be skipped, which makes it useful for little other than debugging the compiler proper.
-feliminate-dwarf2-dups-gdwarf-2. -femit-struct-debug-baseonlyThis option substantially reduces the size of debugging information, but at significant potential loss in type information to the debugger. See -femit-struct-debug-reduced for a less aggressive option. See -femit-struct-debug-detailed for more detailed control.
This option works only with DWARF 2.
-femit-struct-debug-reducedThis option significantly reduces the size of debugging information, with some potential loss in type information to the debugger. See -femit-struct-debug-baseonly for a more aggressive option. See -femit-struct-debug-detailed for more detailed control.
This option works only with DWARF 2.
-femit-struct-debug-detailed[=spec-list]
This option is a detailed version of -femit-struct-debug-reduced and -femit-struct-debug-baseonly, which serves for most needs.
A specification has the syntax [‘dir:’|‘ind:’][‘ord:’|‘gen:’](‘any’|‘sys’|‘base’|‘none’)
The optional first word limits the specification to structs that are used directly (‘dir:’) or used indirectly (‘ind:’). A struct type is used directly when it is the type of a variable, member. Indirect uses arise through pointers to structs. That is, when use of an incomplete struct is valid, the use is indirect. An example is ‘struct one direct; struct two * indirect;’.
The optional second word limits the specification to ordinary structs (‘ord:’) or generic structs (‘gen:’). Generic structs are a bit complicated to explain. For C++, these are non-explicit specializations of template classes, or non-template classes within the above. Other programming languages have generics, but -femit-struct-debug-detailed does not yet implement them.
The third word specifies the source files for those structs for which the compiler should emit debug information. The values ‘none’ and ‘any’ have the normal meaning. The value ‘base’ means that the base of name of the file in which the type declaration appears must match the base of the name of the main compilation file. In practice, this means that when compiling foo.c, debug information is generated for types declared in that file and foo.h, but not other header files. The value ‘sys’ means those types satisfying ‘base’ or declared in system or compiler headers.
You may need to experiment to determine the best settings for your application.
The default is -femit-struct-debug-detailed=all.
This option works only with DWARF 2.
-fno-merge-debug-strings-fdebug-prefix-map=old=new
-fno-dwarf2-cfi-asm.eh_frame section instead of using GAS .cfi_* directives.
-pprof. You must use this option when compiling the source files you want data about, and you must also use it when linking.
-pggprof. You must use this option when compiling the source files you want data about, and you must also use it when linking. -Q-ftime-report-fmem-report-fmem-report-wpa-fpre-ipa-mem-report-fpost-ipa-mem-report-fprofile-report-fstack-usage.su to the auxname. auxname is generated from the name of the output file, if explicitly specified and it is not an executable, otherwise it is the basename of the source file. An entry is made up of three fields: static, dynamic, bounded. The qualifier static means that the function manipulates the stack statically: a fixed number of bytes are allocated for the frame on function entry and released on function exit; no stack adjustments are otherwise made in the function. The second field is this fixed number of bytes.
The qualifier dynamic means that the function manipulates the stack dynamically: in addition to the static allocation described above, stack adjustments are made in the body of the function, for example to push/pop arguments around function calls. If the qualifier bounded is also present, the amount of these adjustments is bounded at compile time and the second field is an upper bound of the total amount of stack used by the function. If it is not present, the amount of these adjustments is not bounded at compile time and the second field only represents the bounded part.
-fprofile-arcs-fbranch-probabilities), or for test coverage analysis (-ftest-coverage). Each object file's auxname is generated from the name of the output file, if explicitly specified and it is not the final executable, otherwise it is the basename of the source file. In both cases any suffix is removed (e.g. foo.gcda for input file dir/foo.c, or dir/foo.gcda for output file specified as -o dir/foo.o). See Cross-profiling.
--coverage-fprofile-arcs -ftest-coverage (when compiling) and -lgcov (when linking). See the documentation for those options for more details. -fprofile-arcs plus optimization and code generation options. For test coverage analysis, use the additional -ftest-coverage option. You do not need to profile every source file in a program. -lgcov or -fprofile-arcs (the latter implies the former). fork calls are detected and correctly handled (double counting will not happen). -fbranch-probabilities (see Options that Control Optimization). gcov to produce human readable information from the .gcno and .gcda files. Refer to the gcov documentation for further information. With -fprofile-arcs, for each function of your program GCC creates a program flow graph, then finds a spanning tree for the graph. Only arcs that are not on the spanning tree have to be instrumented: the compiler adds code to count the number of times that these arcs are executed. When an arc is the only exit or only entrance to a block, the instrumentation code can be added to the block; otherwise, a new basic block must be created to hold the instrumentation code.
-ftest-coveragegcov code-coverage utility (see gcov—a Test Coverage Program) can use to show program coverage. Each source file's note file is called auxname.gcno. Refer to the -fprofile-arcs option above for a description of auxname and instructions on how to generate test coverage data. Coverage data matches the source files more closely if you do not optimize. -fdbg-cnt-list-fdbg-cnt=counter-value-list
UINT_MAX; thus dbg_cnt() returns true always unless the upper bound is set by this option. For example, with -fdbg-cnt=dce:10,tail_call:0, dbg_cnt(dce) returns true only for first 10 invocations. -fenable-kind-pass-fdisable-kind-pass=range-list
-fdisable-ipa-pass
-fdisable-rtl-pass-fdisable-rtl-pass=range-list
-fdump-passes. -fdisable-tree-pass-fdisable-tree-pass=range-list
-fdisable-rtl for the description of option arguments. -fenable-ipa-pass
-fenable-rtl-pass-fenable-rtl-pass=range-list
-fdisable-rtl for option argument description and examples. -fenable-tree-pass-fenable-tree-pass=range-list
-fdisable-rtl for the description of option arguments. Here are some examples showing uses of these options.
# disable ccp1 for all functions -fdisable-tree-ccp1 # disable complete unroll for function whose cgraph node uid is 1 -fenable-tree-cunroll=1 # disable gcse2 for functions at the following ranges [1,1], # [300,400], and [400,1000] # disable gcse2 for functions foo and foo2 -fdisable-rtl-gcse2=foo,foo2 # disable early inlining -fdisable-tree-einline # disable ipa inlining -fdisable-ipa-inline # enable tree full unroll -fenable-tree-unroll
-dletters-fdump-rtl-pass-fdump-rtl-pass=filename
-E is used for preprocessing. Debug dumps can be enabled with a -fdump-rtl switch or some -d option letters. Here are the possible letters for use in pass and letters, and their meanings:
-fdump-rtl-alignments-fdump-rtl-asmcons-fdump-rtl-auto_inc_dec-fdump-rtl-barriers-fdump-rtl-bbpart-fdump-rtl-bbro-fdump-rtl-btl1-fdump-rtl-btl2-fdump-rtl-btl1 and -fdump-rtl-btl2 enable dumping after the two branch target load optimization passes. -fdump-rtl-bypass-fdump-rtl-combine-fdump-rtl-compgotos-fdump-rtl-ce1-fdump-rtl-ce2-fdump-rtl-ce3-fdump-rtl-ce1, -fdump-rtl-ce2, and -fdump-rtl-ce3 enable dumping after the three if conversion passes. -fdump-rtl-cprop_hardreg-fdump-rtl-csa-fdump-rtl-cse1-fdump-rtl-cse2-fdump-rtl-cse1 and -fdump-rtl-cse2 enable dumping after the two common subexpression elimination passes. -fdump-rtl-dce-fdump-rtl-dbr-fdump-rtl-dce1-fdump-rtl-dce2-fdump-rtl-dce1 and -fdump-rtl-dce2 enable dumping after the two dead store elimination passes. -fdump-rtl-eh-fdump-rtl-eh_ranges-fdump-rtl-expand-fdump-rtl-fwprop1-fdump-rtl-fwprop2-fdump-rtl-fwprop1 and -fdump-rtl-fwprop2 enable dumping after the two forward propagation passes. -fdump-rtl-gcse1-fdump-rtl-gcse2-fdump-rtl-gcse1 and -fdump-rtl-gcse2 enable dumping after global common subexpression elimination. -fdump-rtl-init-regs-fdump-rtl-initvals-fdump-rtl-into_cfglayout-fdump-rtl-ira-fdump-rtl-jump-fdump-rtl-loop2-fdump-rtl-loop2 enables dumping after the rtl loop optimization passes. -fdump-rtl-mach-fdump-rtl-mode_sw-fdump-rtl-rnreg-fdump-rtl-outof_cfglayout-fdump-rtl-peephole2-fdump-rtl-postreload-fdump-rtl-pro_and_epilogue-fdump-rtl-sched1-fdump-rtl-sched2-fdump-rtl-sched1 and -fdump-rtl-sched2 enable dumping after the basic block scheduling passes. -fdump-rtl-ree-fdump-rtl-seqabstr-fdump-rtl-shorten-fdump-rtl-sibling-fdump-rtl-split1-fdump-rtl-split2-fdump-rtl-split3-fdump-rtl-split4-fdump-rtl-split5-fdump-rtl-split1, -fdump-rtl-split2, -fdump-rtl-split3, -fdump-rtl-split4 and -fdump-rtl-split5 enable dumping after five rounds of instruction splitting. -fdump-rtl-sms-fdump-rtl-stack-fdump-rtl-subreg1-fdump-rtl-subreg2-fdump-rtl-subreg1 and -fdump-rtl-subreg2 enable dumping after the two subreg expansion passes. -fdump-rtl-unshare-fdump-rtl-vartrack-fdump-rtl-vregs-fdump-rtl-web-fdump-rtl-regclass-fdump-rtl-subregs_of_mode_init-fdump-rtl-subregs_of_mode_finish-fdump-rtl-dfinit-fdump-rtl-dfinish-da-fdump-rtl-all-dA-dD-dH-dp-dP-dp annotation. -dx-fdump-rtl-expand. -fdump-noaddr-fdump-unnumbered-g. -fdump-unnumbered-links-d option above), suppress instruction numbers for the links to the previous and next instructions in a sequence. -fdump-translation-unit (C++ only)-fdump-translation-unit-options (C++ only)
.tu to the source file name, and the file is created in the same directory as the output file. If the ‘-options’ form is used, options controls the details of the dump as described for the -fdump-tree options. -fdump-class-hierarchy (C++ only)-fdump-class-hierarchy-options (C++ only)
.class to the source file name, and the file is created in the same directory as the output file. If the ‘-options’ form is used, options controls the details of the dump as described for the -fdump-tree options. -fdump-ipa-switch
all’cgraph’inline’-fdump-passes-fdump-statistics-option
.statistics’ to the source file name, and the file is created in the same directory as the output file. If the ‘-option’ form is used, ‘-stats’ causes counters to be summed over the whole compilation unit while ‘-details’ dumps every event as the passes generate them. The default with no option is to sum counters for each function compiled. -fdump-tree-switch-fdump-tree-switch-options-fdump-tree-switch-options=filename
-’ separated options which control the details of the dump. Not all options are applicable to all dumps; those that are not meaningful are ignored. The following options are available address’asmname’DECL_ASSEMBLER_NAME has been set for a given decl, use that in the dump instead of DECL_NAME. Its primary use is ease of use working backward from mangled names in the assembly file. slim’When dumping pretty-printed trees, this option inhibits dumping the bodies of control structures.
When dumping RTL, print the RTL in slim (condensed) form instead of the default LISP-like representation.
raw’details’stats’blocks’graph’This option currently only works for RTL dumps, and the RTL is always dumped in slim form.
vops’lineno’uid’DECL_UID) for each variable. verbose’eh’scev’optimized’missed’notes’stdout and stderr are treated specially and are considered already open standard streams. For example, gcc -O2 -ftree-vectorize -fdump-tree-vect-blocks=foo.dump
-fdump-tree-pre=stderr file.c outputs vectorizer dump into foo.dump, while the PRE dump is output on to stderr. If two conflicting dump filenames are given for the same pass, then the latter option overrides the earlier one.
all’raw, slim, verbose and lineno. optall’optimized, missed, and note. The following tree dumps are possible:
original’optimized’gimple’.gimple to the source file name. cfg’.cfg to the source file name. ch’.ch to the source file name. ssa’.ssa to the source file name. alias’.alias to the source file name. ccp’.ccp to the source file name. storeccp’.storeccp to the source file name. pre’.pre to the source file name. fre’.fre to the source file name. copyprop’.copyprop to the source file name. store_copyprop’.store_copyprop to the source file name. dce’.dce to the source file name. sra’.sra to the source file name. sink’.sink to the source file name. dom’.dom to the source file name. dse’.dse to the source file name. phiopt’.phiopt to the source file name. forwprop’.forwprop to the source file name. copyrename’.copyrename to the source file name. nrv’.nrv to the source file name. vect’.vect to the source file name. slp’.slp to the source file name. vrp’.vrp to the source file name. all’-fopt-info-fopt-info-options-fopt-info-options=filename
-’ separated options to select the dump details and optimizations. If options is not specified, it defaults to optimized for details and optall for optimization groups. If the filename is not specified, it defaults to stderr. Note that the output filename will be overwritten in case of multiple translation units. If a combined output from multiple translation units is desired, stderr should be used instead. The options can be divided into two groups, 1) options describing the verbosity of the dump, and 2) options describing which optimizations should be included. The options from both the groups can be freely mixed as they are non-overlapping. However, in case of any conflicts, the latter options override the earlier options on the command line. Though multiple -fopt-info options are accepted, only one of them can have =filename. If other filenames are provided then all but the first one are ignored.
The dump verbosity has the following options
optimized’missed’gcc -O2 -ftree-vectorize -fopt-info-vec-missed
will print information about missed optimization opportunities from vectorization passes on stderr.
note’all’The second set of options describes a group of optimizations and may include one or more of the following.
ipa’loop’inline’vec’optall’For example,
gcc -O3 -fopt-info-missed=missed.all
outputs missed optimization report from all the passes into missed.all.
As another example,
gcc -O3 -fopt-info-inline-optimized-missed=inline.txt
will output information about missed optimizations as well as optimized locations from all the inlining passes into inline.txt.
If the filename is provided, then the dumps from all the applicable optimizations are concatenated into the filename. Otherwise the dump is output onto stderr. If options is omitted, it defaults to all-optall, which means dump all available optimization info from all the passes. In the following example, all optimization info is output on to stderr.
gcc -O3 -fopt-info
Note that -fopt-info-vec-missed behaves the same as -fopt-info-missed-vec.
As another example, consider
gcc -fopt-info-vec-missed=vec.miss -fopt-info-loop-optimized=loop.opt
Here the two output filenames vec.miss and loop.opt are in conflict since only one output file is allowed. In this case, only the first option takes effect and the subsequent options are ignored. Thus only the vec.miss is produced which contains dumps from the vectorizer about missed opportunities.
-frandom-seed=string
-frandom-seed option to produce reproducibly identical object files. The string should be different for every file you compile.
-fsched-verbose=n
-fdump-rtl-sched1 or -fdump-rtl-sched2 is specified, in which case it is output to the usual dump listing file, .sched1 or .sched2 respectively. However for n greater than nine, the output is always printed to standard error. For n greater than zero, -fsched-verbose outputs the same information as -fdump-rtl-sched1 and -fdump-rtl-sched2. For n greater than one, it also output basic block probabilities, detailed ready list information and unit/insn info. For n greater than two, it includes RTL at abort point, control-flow and regions info. And for n over four, -fsched-verbose also includes dependence info.
-save-temps-save-temps=cwdfoo.c with -c -save-temps produces files foo.i and foo.s, as well as foo.o. This creates a preprocessed foo.i output file even though the compiler now normally uses an integrated preprocessor. When used in combination with the -x command-line option, -save-temps is sensible enough to avoid over writing an input source file with the same extension as an intermediate file. The corresponding intermediate file may be obtained by renaming the source file before using -save-temps.
If you invoke GCC in parallel, compiling several different source files that share a common base name in different subdirectories or the same source file compiled for multiple output destinations, it is likely that the different parallel compilers will interfere with each other, and overwrite the temporary files. For instance:
gcc -save-temps -o outdir1/foo.o indir1/foo.c& gcc -save-temps -o outdir2/foo.o indir2/foo.c&
may result in foo.i and foo.o being written to simultaneously by both compilers.
-save-temps=obj-o option is used, the temporary files are based on the object file. If the -o option is not used, the -save-temps=obj switch behaves like -save-temps. For example:
gcc -save-temps=obj -c foo.c gcc -save-temps=obj -c bar.c -o dir/xbar.o gcc -save-temps=obj foobar.c -o dir2/yfoobar
creates foo.i, foo.s, dir/xbar.i, dir/xbar.s, dir2/yfoobar.i, dir2/yfoobar.s, and dir2/yfoobar.o.
-time[=file]
Without the specification of an output file, the output looks like this:
# cc1 0.12 0.01 # as 0.00 0.01
The first number on each line is the “user time”, that is time spent executing the program itself. The second number is “system time”, time spent executing operating system routines on behalf of the program. Both numbers are in seconds.
With the specification of an output file, the output is appended to the named file, and it looks like this:
0.12 0.01 cc1 options 0.00 0.01 as options
The “user time” and the “system time” are moved before the program name, and the options passed to the program are displayed, so that one can later tell what file was being compiled, and with which options.
-fvar-trackingIt is enabled by default when compiling with optimization (-Os, -O, -O2, ...), debugging information (-g) and the debug info format supports it.
-fvar-tracking-assignments-gdwarf-4 is recommended along with it. It can be enabled even if var-tracking is disabled, in which case annotations are created and maintained, but discarded at the end.
-fvar-tracking-assignments-toggle-fvar-tracking-assignments, in the same way that -gtoggle toggles -g. -print-file-name=library
-print-multi-directoryGCC_EXEC_PREFIX. -print-multi-lib;’, and each switch starts with an ‘@’ instead of the ‘-’, without spaces between multiple switches. This is supposed to ease shell processing. -print-multi-os-directorylib subdirectory. If OS libraries are present in the lib subdirectory and no multilibs are used, this is usually just ., if OS libraries are present in libsuffix sibling directories this prints e.g. ../lib64, ../lib or ../lib32, or if OS libraries are present in lib/subdir subdirectories it prints e.g. amd64, sparcv9 or ev6. -print-multiarchlib subdirectory. -print-prog-name=program
-print-file-name, but searches for a program such as ‘cpp’. -print-libgcc-file-name-print-file-name=libgcc.a. This is useful when you use -nostdlib or -nodefaultlibs but you do want to link with libgcc.a. You can do:
gcc -nostdlib files... `gcc -print-libgcc-file-name`
-print-search-dirsgcc searches—and don't do anything else. This is useful when gcc prints the error message ‘installation problem, cannot exec cpp0: No such file or directory’. To resolve this you either need to put cpp0 and the other compiler components where gcc expects to find them, or you can set the environment variable GCC_EXEC_PREFIX to the directory where you installed them. Don't forget the trailing ‘/’. See Environment Variables.
-print-sysroot--sysroot option, possibly with an extra suffix that depends on compilation options. If no target sysroot is specified, the option prints nothing. -print-sysroot-headers-suffix-dumpmachinei686-pc-linux-gnu’)—and don't do anything else. -dumpversion3.0’)—and don't do anything else. -dumpspecs-fno-eliminate-unused-debug-types
© Free Software Foundation
Licensed under the GNU Free Documentation License, Version 1.3.
https://gcc.gnu.org/onlinedocs/gcc-4.9.3/gcc/Debugging-Options.html