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GNU CC has various special options that are used for debugging
either your program or gcc
:
-g
- Produce debugging information in the operating system's native format
(stabs, COFF, XCOFF, or DWARF). GDB can work with this debugging
information.
On 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 will probably make 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', `-gdwarf+', or `-gdwarf'
(see below).
Unlike most other C compilers, GNU CC 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 were already at hand; some statements may
execute in different places because they were 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 GNU CC is generated with the
capability for more than one debugging format.
-ggdb
- Produce debugging information in the native format (if that is supported),
including GDB extensions if at all possible.
-gstabs
- Produce debugging information in stabs format (if that is supported),
without GDB extensions. This is the format used by DBX on most BSD
systems. On MIPS, Alpha and System V Release 4 systems this option
produces stabs debugging output which is not understood by DBX or SDB.
On System V Release 4 systems this option requires the GNU assembler.
-gstabs+
- Produce debugging information in stabs format (if that is supported),
using GNU extensions understood only by the GNU debugger (GDB). The
use of these extensions is likely to make other debuggers crash or
refuse to read the program.
-gcoff
- Produce debugging information in COFF format (if that is supported).
This is the format used by SDB on most System V systems prior to
System V Release 4.
-gxcoff
- Produce debugging information in XCOFF format (if that is supported).
This is the format used by the DBX debugger on IBM RS/6000 systems.
-gxcoff+
- Produce debugging information in XCOFF format (if that is supported),
using GNU extensions understood only by the GNU debugger (GDB). The
use of these extensions is likely to make other debuggers crash or
refuse to read the program, and may cause assemblers other than the GNU
assembler (GAS) to fail with an error.
-gdwarf
- Produce debugging information in DWARF format (if that is supported).
This is the format used by SDB on most System V Release 4 systems.
-gdwarf+
- Produce debugging information in DWARF format (if that is supported),
using GNU extensions understood only by the GNU debugger (GDB). The
use of these extensions is likely to make other debuggers crash or
refuse to read the program.
-glevel
-ggdblevel
-gstabslevel
-gcofflevel
-gxcofflevel
-gdwarflevel
- Request debugging information and also use level to specify how
much information. The default level is 2.
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, but no information
about local variables and no line numbers.
Level 3 includes extra information, such as all the macro definitions
present in the program. Some debuggers support macro expansion when
you use `-g3'.
-p
- Generate extra code to write profile information suitable for the
analysis program
prof
. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
-pg
- Generate extra code to write profile information suitable for the
analysis program
gprof
. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
-a
- Generate extra code to write profile information for basic blocks, which will
record the number of times each basic block is executed, the basic block start
address, and the function name containing the basic block. If `-g' is
used, the line number and filename of the start of the basic block will also be
recorded. If not overridden by the machine description, the default action is
to append to the text file `bb.out'.
This data could be analyzed by a program like
tcov
. Note,
however, that the format of the data is not what tcov
expects.
Eventually GNU gprof
should be extended to process this data.
-fprofile-arcs
- Instrument arcs during compilation. For each function of your
program, GNU CC 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.
Since not every arc in the program must be instrumented, programs
compiled with this option run faster than programs compiled with
`-a', which adds instrumentation code to every basic block in the
program. The tradeoff: since
gcov
does not have
execution counts for all branches, it must start with the execution
counts for the instrumented branches, and then iterate over the program
flow graph until the entire graph has been solved. Hence, gcov
runs a little more slowly than a program which uses information from
`-a'.
`-fprofile-arcs' also makes it possible to estimate branch
probabilities, and to calculate basic block execution counts. In
general, basic block execution counts do not give enough information to
estimate all branch probabilities. When the compiled program exits, it
saves the arc execution counts to a file called
`sourcename.da'. Use the compiler option
`-fbranch-probabilities' (see section Options That Control Optimization) when recompiling, to optimize using estimated
branch probabilities.
-ftest-coverage
- Create data files for the
gcov
code-coverage utility
(see section gcov
: a Test Coverage Program).
The data file names begin with the name of your source file:
sourcename.bb
- A mapping from basic blocks to line numbers, which
gcov
uses to
associate basic block execution counts with line numbers.
sourcename.bbg
- A list of all arcs in the program flow graph. This allows
gcov
to reconstruct the program flow graph, so that it can compute all basic
block and arc execution counts from the information in the
sourcename.da
file (this last file is the output from
`-fprofile-arcs').
-dletters
- Says to make debugging dumps during compilation at times specified by
letters. This is used for debugging the compiler. The file names
for most of the dumps are made by appending a word to the source file
name (e.g. `foo.c.rtl' or `foo.c.jump'). Here are the
possible letters for use in letters, and their meanings:
- `M'
- Dump all macro definitions, at the end of preprocessing, and write no
output.
- `N'
- Dump all macro names, at the end of preprocessing.
- `D'
- Dump all macro definitions, at the end of preprocessing, in addition to
normal output.
- `y'
- Dump debugging information during parsing, to standard error.
- `r'
- Dump after RTL generation, to `file.rtl'.
- `x'
- Just generate RTL for a function instead of compiling it. Usually used
with `r'.
- `j'
- Dump after first jump optimization, to `file.jump'.
- `s'
- Dump after CSE (including the jump optimization that sometimes
follows CSE), to `file.cse'.
- `L'
- Dump after loop optimization, to `file.loop'.
- `t'
- Dump after the second CSE pass (including the jump optimization that
sometimes follows CSE), to `file.cse2'.
- `f'
- Dump after flow analysis, to `file.flow'.
- `c'
- Dump after instruction combination, to the file
`file.combine'.
- `S'
- Dump after the first instruction scheduling pass, to
`file.sched'.
- `l'
- Dump after local register allocation, to
`file.lreg'.
- `g'
- Dump after global register allocation, to
`file.greg'.
- `R'
- Dump after the second instruction scheduling pass, to
`file.sched2'.
- `J'
- Dump after last jump optimization, to
`file.jump2'.
- `d'
- Dump after delayed branch scheduling, to `file.dbr'.
- `k'
- Dump after conversion from registers to stack, to `file.stack'.
- `a'
- Produce all the dumps listed above.
- `m'
- Print statistics on memory usage, at the end of the run, to
standard error.
- `p'
- Annotate the assembler output with a comment indicating which
pattern and alternative was used.
-fpretend-float
- When running a cross-compiler, pretend that the target machine uses the
same floating point format as the host machine. This causes incorrect
output of the actual floating constants, but the actual instruction
sequence will probably be the same as GNU CC would make when running on
the target machine.
-save-temps
- Store the usual "temporary" intermediate files permanently; place them
in the current directory and name them based on the source file. Thus,
compiling `foo.c' with `-c -save-temps' would produce files
`foo.i' and `foo.s', as well as `foo.o'.
-print-file-name=library
- Print the full absolute name of the library file library that
would be used when linking--and don't do anything else. With this
option, GNU CC does not compile or link anything; it just prints the
file name.
-print-prog-name=program
- Like `-print-file-name', but searches for a program such as `cpp'.
-print-libgcc-file-name
- Same as `-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-dirs
- Print the name of the configured installation directory and a list of
program and library directories
gcc
will search--and don't do anything else.
This is useful when gcc
prints the error message
installation problem, cannot exec cpp:
No such file or directory
To resolve this you either need to put `cpp' 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 section Environment Variables Affecting GNU CC.
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