[PATCH v2] strip: Treat slim GCC/LLVM IR objects the same
H.J. Lu
hjl.tools@gmail.com
Fri Aug 15 01:11:22 GMT 2025
On Thu, Aug 14, 2025 at 4:07 PM Alan Modra <amodra@gmail.com> wrote:
>
> On Thu, Aug 14, 2025 at 03:27:54PM -0700, H.J. Lu wrote:
> > Slim LLVM IR object is a standalone file whose first 4 bytes are 'B',
> > 'C', 0xc0, 0xde. GCC IR object is regular ELF object with sections
> > whose names start with .gnu.lto_.* or .gnu.debuglto_.*. GCC IR object
> > uses a .gnu.lto_.lto.<some_hash> section to encode the LTO bytecode
> > information:
> >
> > struct lto_section
> > {
> > int16_t major_version;
> > int16_t minor_version;
> > unsigned char slim_object;
> >
> > /* Flags is a private field that is not defined publicly. */
> > uint16_t flags;
> > };
> >
> > In slim GCC IR object, the slim_object field is non-zero. Strip should
> > treat slim GCC/LLVM IR objects the same. Since strip won't change slim
> > LLVM IR objects, it should leave slim GCC IR object unchanged even when
> > asked to remove all IR objects:
> >
> > 1. Set the lto_type field to lto_slim_ir_object for slim LLVM IR object.
> > 2. Always copy slim IR object as unknown object.
>
> OK. Please also move lto_sections_removed from file scope.
Will do.
Thanks.
> > bfd/
> >
> > PR binutils/33271
> > * format.c (bfd_set_lto_type): Set the lto_type field to
> > lto_slim_ir_object for slim LLVM IR object.
> >
> > binutils/
> >
> > PR binutils/33271
> > * objcopy.c (copy_archive): Always copy slim IR object as unknown
> > object.
> > (copy_file): Likewise.
> >
> > ld/
> >
> > PR binutils/33271
> > * testsuite/ld-plugin/lto-binutils.exp: Don't check if fat IR is
> > available when running slim IR tests.
> > * testsuite/ld-plugin/strip-1a-s-all.nd: Expect full symbol list.
> >
> > Signed-off-by: H.J. Lu <hjl.tools@gmail.com>
> > ---
> > bfd/format.c | 66 +++++++++++++++---------
> > binutils/objcopy.c | 10 ++--
> > ld/testsuite/ld-plugin/lto-binutils.exp | 34 ++++++------
> > ld/testsuite/ld-plugin/strip-1a-s-all.nd | 5 +-
> > 4 files changed, 65 insertions(+), 50 deletions(-)
> >
> > diff --git a/bfd/format.c b/bfd/format.c
> > index 25feb5266df..b74c6240f23 100644
> > --- a/bfd/format.c
> > +++ b/bfd/format.c
> > @@ -376,33 +376,49 @@ bfd_set_lto_type (bfd *abfd ATTRIBUTE_UNUSED)
> > | (bfd_get_flavour (abfd) == bfd_target_elf_flavour
> > ? EXEC_P : 0))) == 0)
> > {
> > - asection *sec;
> > + asection *sec = abfd->sections;
> > enum bfd_lto_object_type type = lto_non_ir_object;
> > - struct lto_section lsection = { 0, 0, 0, 0 };
> > - /* GCC uses .gnu.lto_.lto.<some_hash> as a LTO bytecode information
> > - section. */
> > - for (sec = abfd->sections; sec != NULL; sec = sec->next)
> > - if (strcmp (sec->name, GNU_OBJECT_ONLY_SECTION_NAME) == 0)
> > - {
> > - type = lto_mixed_object;
> > - abfd->object_only_section = sec;
> > - break;
> > - }
> > - else if (strcmp (sec->name, ".llvm.lto") == 0)
> > - {
> > - type = lto_fat_ir_object;
> > - break;
> > - }
> > - else if (lsection.major_version == 0
> > - && startswith (sec->name, ".gnu.lto_.lto.")
> > - && bfd_get_section_contents (abfd, sec, &lsection, 0,
> > - sizeof (struct lto_section)))
> > - {
> > - if (lsection.slim_object)
> > - type = lto_slim_ir_object;
> > - else
> > - type = lto_fat_ir_object;
> > + if (sec == NULL)
> > + {
> > + /* If there are no sections, check for slim LLVM IR object whose
> > + first 4 bytes are: 'B', 'C', 0xc0, 0xde. */
> > + bfd_byte llvm_ir_magic[4];
> > + if (bfd_seek (abfd, 0, SEEK_SET) == 0
> > + && bfd_read (llvm_ir_magic, 4, abfd) == 4
> > + && llvm_ir_magic[0] == 'B'
> > + && llvm_ir_magic[1] == 'C'
> > + && llvm_ir_magic[2] == 0xc0
> > + && llvm_ir_magic[3] == 0xde)
> > + type = lto_slim_ir_object;
> > + }
> > + else
> > + {
> > + struct lto_section lsection = { 0, 0, 0, 0 };
> > + /* GCC uses .gnu.lto_.lto.<some_hash> as a LTO bytecode
> > + information section. */
> > + for (; sec != NULL; sec = sec->next)
> > + if (strcmp (sec->name, GNU_OBJECT_ONLY_SECTION_NAME) == 0)
> > + {
> > + type = lto_mixed_object;
> > + abfd->object_only_section = sec;
> > + break;
> > + }
> > + else if (strcmp (sec->name, ".llvm.lto") == 0)
> > + {
> > + type = lto_fat_ir_object;
> > + break;
> > + }
> > + else if (lsection.major_version == 0
> > + && startswith (sec->name, ".gnu.lto_.lto.")
> > + && bfd_get_section_contents (abfd, sec, &lsection, 0,
> > + sizeof (struct lto_section)))
> > + {
> > + if (lsection.slim_object)
> > + type = lto_slim_ir_object;
> > + else
> > + type = lto_fat_ir_object;
> > }
> > + }
> >
> > abfd->lto_type = type;
> > }
> > diff --git a/binutils/objcopy.c b/binutils/objcopy.c
> > index bc07176799a..cb894ca9262 100644
> > --- a/binutils/objcopy.c
> > +++ b/binutils/objcopy.c
> > @@ -3765,9 +3765,8 @@ copy_archive (bfd *ibfd, bfd *obfd, const char *output_target,
> > }
> >
> > #if BFD_SUPPORTS_PLUGINS
> > - /* Copy LTO IR file as unknown object. */
> > - if (!lto_sections_removed
> > - && this_element->lto_type == lto_slim_ir_object)
> > + /* Copy slim LTO IR file as unknown object. */
> > + if (this_element->lto_type == lto_slim_ir_object)
> > ok_object = false;
> > #endif
> > if (ok_object)
> > @@ -4066,9 +4065,8 @@ copy_file (const char *input_filename, const char *output_filename, int ofd,
> > }
> >
> > #if BFD_SUPPORTS_PLUGINS
> > - /* Copy LTO IR file as unknown object. */
> > - if (!lto_sections_removed
> > - && ibfd->lto_type == lto_slim_ir_object)
> > + /* Copy slim LTO IR file as unknown file. */
> > + if (ibfd->lto_type == lto_slim_ir_object)
> > ok_object = false;
> > #endif
> > if (ok_object
> > diff --git a/ld/testsuite/ld-plugin/lto-binutils.exp b/ld/testsuite/ld-plugin/lto-binutils.exp
> > index 4970e2282cb..1e156e4fc78 100644
> > --- a/ld/testsuite/ld-plugin/lto-binutils.exp
> > +++ b/ld/testsuite/ld-plugin/lto-binutils.exp
> > @@ -254,24 +254,22 @@ run_lto_binutils_test [list \
> > ] \
> > ]
> >
> > -if { [check_lto_fat_available] } {
> > - run_lto_binutils_test [list \
> > - [list \
> > - "strip" \
> > - "-R .gnu.*lto_* -N __gnu_lto_v1" \
> > - "strip-1a.o" \
> > - "strip-1a-s-all.o" \
> > - {{nm -n strip-1a-s-all.nd}} \
> > - ] \
> > - [list \
> > - "strip" \
> > - "-R .gnu.*lto_* -N __gnu_lto_v1" \
> > - "libstrip-1a.a" \
> > - "libstrip-1a-s-all.a" \
> > - {{nm -n strip-1a-s-all.nd}} \
> > - ] \
> > - ]
> > -}
> > +run_lto_binutils_test [list \
> > + [list \
> > + "strip" \
> > + "-R .gnu.*lto_* -N __gnu_lto_v1" \
> > + "strip-1a.o" \
> > + "strip-1a-s-all.o" \
> > + {{nm -n strip-1a-s-all.nd}} \
> > + ] \
> > + [list \
> > + "strip" \
> > + "-R .gnu.*lto_* -N __gnu_lto_v1" \
> > + "libstrip-1a.a" \
> > + "libstrip-1a-s-all.a" \
> > + {{nm -n strip-1a-s-all.nd}} \
> > + ] \
> > +]
> >
> > run_cc_link_tests [list \
> > [list \
> > diff --git a/ld/testsuite/ld-plugin/strip-1a-s-all.nd b/ld/testsuite/ld-plugin/strip-1a-s-all.nd
> > index 612ba6a39b1..52265c2eb3d 100644
> > --- a/ld/testsuite/ld-plugin/strip-1a-s-all.nd
> > +++ b/ld/testsuite/ld-plugin/strip-1a-s-all.nd
> > @@ -1,3 +1,6 @@
> > #...
> > -[0-9a-f]* C _?__gnu_lto_slim
> > + + U foo2
> > + + U foo3
> > +0+ T foo1
> > +0+ T main
> > #pass
> > --
> > 2.50.1
>
> --
> Alan Modra
--
H.J.
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