[PATCH] objdump: allow to display instructions only for given label

Masatake YAMATO

2018-10-22 19:40:26 UTC

This change introduces "label" option argument to "--disassemble"
option. If the label is given, objdump displays instructions only
for the label. This helps you to read a specified area of a
large library quicly.

Following shows how the change works:

(Show the instructions of getenv in glibc)

$ binutils/objdump --disassemble=getenv /lib64/libc.so.6

/lib64/libc.so.6: file format elf64-x86-64

Disassembly of section .plt:

Disassembly of section .text:

0000000000038c50 <getenv>:
38c50: 41 57 push %r15
38c52: 41 56 push %r14
38c54: 41 55 push %r13
...

(Use the label option argument with demangled name)

$ cat /tmp/foo.cc
int
foo(int i)
{
return i + 1;
}

int
main(void)
{
return foo(3);
}
$ gcc -c -g -O0 /tmp/foo.cc
$ nm --demangle ./foo.o
000000000000000f T main
0000000000000000 T foo(int)
$ ./binutils/objdump --demangle --disassemble='foo(int)' ./foo.o

./foo.o: file format elf64-x86-64

Disassembly of section .text:

0000000000000000 <foo(int)>:
0: 55 push %rbp
1: 48 89 e5 mov %rsp,%rbp
4: 89 7d fc mov %edi,-0x4(%rbp)
7: 8b 45 fc mov -0x4(%rbp),%eax
a: 83 c0 01 add $0x1,%eax
d: 5d pop %rbp
e: c3 retq

* objdump.c (long_options): make --disassemble option take
option argument.
(usage): Add description for `label' option argument
for the --disassemble option.
(label): New file private variable.
(struct objdump_disasm_info): New field `label'.
(disassemble_section): Introduce `do_print' local variable
to control whether objdump displays the result of disassembling
for a lable or not.
(main): Set `label' file private variable if the option argument
for the --disassemble option is given.

* doc/binutils.texi (objdump): Add description for the option
argument.

Signed-off-by: Masatake YAMATO <***@redhat.com>
---
binutils/ChangeLog | 17 +++++++++++++++++
binutils/doc/binutils.texi | 5 +++--
binutils/objdump.c | 39 ++++++++++++++++++++++++++++++++------
3 files changed, 53 insertions(+), 8 deletions(-)

diff --git a/binutils/ChangeLog b/binutils/ChangeLog
index e3bbbc3a84..1ca2fe6918 100644
--- a/binutils/ChangeLog
+++ b/binutils/ChangeLog
@@ -1,3 +1,20 @@
+2018-10-23 Masatake YAMATO <***@redhat.com>
+
+ * objdump.c (long_options): make --disassemble option take
+ option argument.
+ (usage): Add description for `label' option argument
+ for the --disassemble option.
+ (label): New file private variable.
+ (struct objdump_disasm_info): New field `label'.
+ (disassemble_section): Introduce `do_print' local variable
+ to control whether objdump displays the result of disassembling
+ for a lable or not.
+ (main): Set `label' file private variable if the option argument
+ for the --disassemble option is given.
+
+ * doc/binutils.texi (objdump): Add description for the option
+ argument.
+
2018-10-18 Nick Clifton <***@redhat.com>

* doc/binutils.texi (readelf): Document alternatives to the
diff --git a/binutils/doc/binutils.texi b/binutils/doc/binutils.texi
index 6edd7b1ae8..66b9a5602b 100644
--- a/binutils/doc/binutils.texi
+++ b/binutils/doc/binutils.texi
@@ -2063,7 +2063,7 @@ ld(1), objdump(1), and the Info entries for @file{binutils}.
objdump [@option{-a}|@option{--archive-headers}]
[@option{-b} @var{bfdname}|@option{--target=@var{bfdname}}]
[@option{-C}|@option{--demangle}[=@var{style}] ]
- [@option{-d}|@option{--disassemble}]
+ [@option{-d}|@option{--disassemble}[=@var{label}]]
[@option{-D}|@option{--disassemble-all}]
[@option{-z}|@option{--disassemble-zeroes}]
[@option{-EB}|@option{-EL}|@option{--endian=}@{big | little @}]
@@ -2193,7 +2193,8 @@ with ctags tool.
@cindex machine instructions
Display the assembler mnemonics for the machine instructions from
@var{objfile}. This option only disassembles those sections which are
-expected to contain instructions.
+expected to contain instructions. If @var{label} is given, display
+the assembler mnemonics only for @var{label}.

@item -D
@itemx --disassemble-all
diff --git a/binutils/objdump.c b/binutils/objdump.c
index 9c3bce8b75..56384b3dfa 100644
--- a/binutils/objdump.c
+++ b/binutils/objdump.c
@@ -118,6 +118,7 @@ static const char *prefix; /* --prefix */
static int prefix_strip; /* --prefix-strip */
static size_t prefix_length;
static bfd_boolean unwind_inlines; /* --inlines. */
+static const char *label;

/* A structure to record the sections mentioned in -j switches. */
struct only
@@ -145,6 +146,7 @@ struct objdump_disasm_info
long dynrelcount;
disassembler_ftype disassemble_fn;
arelent * reloc;
+ const char * label;
};

/* Architecture to disassemble for, or default if NULL. */
@@ -207,7 +209,8 @@ usage (FILE *stream, int status)
-P, --private=OPT,OPT... Display object format specific contents\n\
-h, --[section-]headers Display the contents of the section headers\n\
-x, --all-headers Display the contents of all headers\n\
- -d, --disassemble Display assembler contents of executable sections\n\
+ -d, --disassemble[=label]\n\
+ Display assembler contents of executable sections\n\
-D, --disassemble-all Display assembler contents of all sections\n\
-S, --source Intermix source code with disassembly\n\
-s, --full-contents Display the full contents of all sections requested\n\
@@ -313,7 +316,7 @@ static struct option long_options[]=
{"debugging", no_argument, NULL, 'g'},
{"debugging-tags", no_argument, NULL, 'e'},
{"demangle", optional_argument, NULL, 'C'},
- {"disassemble", no_argument, NULL, 'd'},
+ {"disassemble", optional_argument, NULL, 'd'},
{"disassemble-all", no_argument, NULL, 'D'},
{"disassembler-options", required_argument, NULL, 'M'},
{"disassemble-zeroes", no_argument, NULL, 'z'},
@@ -2253,6 +2256,7 @@ disassemble_section (bfd *abfd, asection *section, void *inf)
asymbol *nextsym;
bfd_vma nextstop_offset;
bfd_boolean insns;
+ bfd_boolean do_print = TRUE;

addr = section->vma + addr_offset;
addr = ((addr & ((sign_adjust << 1) - 1)) ^ sign_adjust) - sign_adjust;
@@ -2278,7 +2282,23 @@ disassemble_section (bfd *abfd, asection *section, void *inf)
pinfo->symtab_pos = -1;
}

- if (! prefix_addresses)
+ if (sym && paux->label)
+ {
+ const char *name = bfd_asymbol_name (sym);
+ char *alloc = NULL;
+ if (do_demangle && name[0] != '\0')
+ {
+ /* Demangle the name. */
+ alloc = bfd_demangle (abfd, name, DMGL_ANSI | DMGL_PARAMS);
+ if (alloc != NULL)
+ name = alloc;
+ }
+ do_print = streq (name, paux->label);
+ if (alloc != NULL)
+ free (alloc);
+ }
+
+ if (! prefix_addresses && do_print)
{
pinfo->fprintf_func (pinfo->stream, "\n");
objdump_print_addr_with_sym (abfd, section, sym, addr,
@@ -2339,9 +2359,14 @@ disassemble_section (bfd *abfd, asection *section, void *inf)
else
insns = FALSE;

- disassemble_bytes (pinfo, paux->disassemble_fn, insns, data,
- addr_offset, nextstop_offset,
- rel_offset, &rel_pp, rel_ppend);
+ if (do_print)
+ {
+ disassemble_bytes (pinfo, paux->disassemble_fn, insns, data,
+ addr_offset, nextstop_offset,
+ rel_offset, &rel_pp, rel_ppend);
+ if (paux->label)
+ break;
+ }

addr_offset = nextstop_offset;
sym = nextsym;
@@ -2394,6 +2419,7 @@ disassemble_data (bfd *abfd)
aux.dynrelbuf = NULL;
aux.dynrelcount = 0;
aux.reloc = NULL;
+ aux.label = label;

disasm_info.print_address_func = objdump_print_address;
disasm_info.symbol_at_address_func = objdump_symbol_at_address;
@@ -3995,6 +4021,7 @@ main (int argc, char **argv)
case 'd':
disassemble = TRUE;
seenflag = TRUE;
+ label = optarg;
break;
case 'z':
disassemble_zeroes = TRUE;

--
2.17.2