GCC has various special options that are used for debugging either your program or GCC:
-g
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-1+
, -gdwarf-1
,
or -gvms
(see below).
Unlike most other C compilers, 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 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 GCC is generated with the
capability for more than one debugging format.
-ggdb
-gstabs
-gstabs+
-gcoff
-gxcoff
-gxcoff+
-gdwarf
-gdwarf+
-gdwarf-2
-gvms
-g
level
-ggdb
level
-gstabs
level
-gcoff
level
-gxcoff
level
-gvms
level
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
.
Note that in order to avoid confusion between DWARF1 debug level 2,
and DWARF2, neither -gdwarf
nor -gdwarf-2
accept
a concatenated debug level. Instead use an additional -g
level
option to change the debug level for DWARF1 or DWARF2.
-p
prof
. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
-pg
gprof
. You must use this option when compiling
the source files you want data about, and you must also use it when
linking.
-a
-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.
-Q
-ftime-report
-fmem-report
-fprofile-arcs
sourcename.da
for each source file.
For profile-directed block ordering, compile the program with
-fprofile-arcs
plus optimization and code generation options,
generate the arc profile information by running the program on a
selected workload, and then compile the program again with the same
optimization and code generation options plus
-fbranch-probabilities
(see Options that Control Optimization).
The other use of -fprofile-arcs
is for use with gcov
,
when it is used with the -ftest-coverage
option.
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-coverage
gcov
code-coverage utility
(see gcov
: a GCC Test Coverage Program).
The data file names begin with the name of your source file:
sourcename.bb
gcov
uses to
associate basic block execution counts with line numbers.
sourcename.bbg
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.
Use -ftest-coverage
with -fprofile-arcs
; the latter
option adds instrumentation to the program, which then writes
execution counts to another data file:
sourcename.da
sourcename.bbg
.
Coverage data will map better to the source files if
-ftest-coverage
is used without optimization.
-d
letters
foo.c.00.rtl
or foo.c.01.sibling
).
Here are the possible letters for use in letters, and their meanings:
A
b
file.14.bp
.
B
file.29.bbro
.
c
file.16.combine
.
C
file.17.ce
.
d
file.31.dbr
.
D
e
file.04.ssa
and
file.07.ussa
.
E
file.26.ce2
.
f
file.15.life
.
F
ADDRESSOF
codes, to
file.09.addressof
.
g
file.21.greg
.
h
file.02.eh
.
k
file.28.stack
.
o
file.22.postreload
.
G
file.10.gcse
.
i
file.01.sibling
.
j
file.03.jump
.
k
file.32.stack
.
l
file.20.lreg
.
L
file.11.loop
.
M
file.30.mach
.
n
file.25.rnreg
.
N
file.18.regmove
.
r
file.00.rtl
.
R
file.27.sched2
.
s
file.08.cse
.
S
file.19.sched
.
t
file.12.cse2
.
w
file.23.flow2
.
X
file.06.ssadce
.
z
file.24.peephole2
.
a
m
p
P
-dp
annotation.
v
file.00.rtl
), dump a representation of the control flow graph
suitable for viewing with VCG to
file.
pass.vcg
.
x
r
.
y
-fdump-unnumbered
-d
option above), suppress instruction
numbers and line number note output. This makes it more feasible to
use diff on debugging dumps for compiler invocations with different
options, in particular with and without -g
.
-fdump-translation-unit
(C and C++ only)
-fdump-translation-unit-
options
(C and C++ only)
.tu
to the
source file name. 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. If the -
options
form is used,
options controls the details of the dump as described for the
-fdump-tree
options.
-fdump-tree-
switch
(C++ only)
-fdump-tree-
switch-
options
(C++ only)
-
options
form is used, options is a list of -
separated options that
control the details of the dump. Not all options are applicable to all
dumps, those which are not meaningful will be ignored. The following
options are available
address
slim
all
The following tree dumps are possible:
original
file.original
.
optimized
file.optimized
.
inlined
file.inlined
.
-fsched-verbose=
n
-dS
or -dR
is
specified, in which case it is output to the usual dump
listing file, .sched
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 -dRS
. 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.
-fpretend-float
-save-temps
foo.c
with -c -save-temps
would produce 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.
-time
# 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.
-print-file-name=
library
-print-multi-directory
GCC_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-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-dirs
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.
-dumpmachine
i686-pc-linux-gnu
)--and don't do anything else.
-dumpversion
3.0
)--and don't do
anything else.
-dumpspecs