[PATCH v2 1/2] bfd/ELF: restrict file alignment for object files
Jan Beulich
jbeulich@suse.com
Fri Oct 4 07:31:02 GMT 2024
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Fri Oct 4 07:31:02 GMT 2024
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While for executables properly aligning sections within the file can be
quite relevant, the same is of pretty little importance for relocatable
object files. Avoid passing "true" into
_bfd_elf_assign_file_position_for_section() when dealing with object
files, but compensate minimally by applying log_file_align in such
cases as a cap to the alignment put in place.
---
RFC: Question is whether this minimal alignment shouldn't be applied in
all cases, i.e. also when incoming "align" is "true".
The Arm64 test being adjusted has an imo misleading name: I first
thought I broke something. Only when going back to the commit that
introduced it, I found that the test is about the _absence_ of tail
padding. Would people mind if I inserted e.g. "no" on the #name line?
---
v2: Replace heuristic in _bfd_elf_assign_file_position_for_section().
--- a/bfd/elf.c
+++ b/bfd/elf.c
@@ -4562,10 +4562,23 @@ align_file_position (file_ptr off, int a
file_ptr
_bfd_elf_assign_file_position_for_section (Elf_Internal_Shdr *i_shdrp,
file_ptr offset,
- bool align)
+ bool align,
+ unsigned char log_file_align)
{
- if (align && i_shdrp->sh_addralign > 1)
- offset = BFD_ALIGN (offset, i_shdrp->sh_addralign & -i_shdrp->sh_addralign);
+ if (i_shdrp->sh_addralign > 1)
+ {
+ file_ptr salign = i_shdrp->sh_addralign & -i_shdrp->sh_addralign;
+
+ if (align)
+ offset = BFD_ALIGN (offset, salign);
+ else if (log_file_align)
+ {
+ /* Heuristic: Cap alignment at log_file_align. */
+ file_ptr falign = 1u << log_file_align;
+
+ offset = BFD_ALIGN (offset, salign < falign ? salign : falign);
+ }
+ }
i_shdrp->sh_offset = offset;
if (i_shdrp->bfd_section != NULL)
i_shdrp->bfd_section->filepos = offset;
@@ -4653,18 +4666,18 @@ _bfd_elf_compute_section_file_positions
off = elf_next_file_pos (abfd);
hdr = & elf_symtab_hdr (abfd);
- off = _bfd_elf_assign_file_position_for_section (hdr, off, true);
+ off = _bfd_elf_assign_file_position_for_section (hdr, off, true, 0);
if (elf_symtab_shndx_list (abfd) != NULL)
{
hdr = & elf_symtab_shndx_list (abfd)->hdr;
if (hdr->sh_size != 0)
- off = _bfd_elf_assign_file_position_for_section (hdr, off, true);
+ off = _bfd_elf_assign_file_position_for_section (hdr, off, true, 0);
/* FIXME: What about other symtab_shndx sections in the list ? */
}
hdr = &elf_tdata (abfd)->strtab_hdr;
- off = _bfd_elf_assign_file_position_for_section (hdr, off, true);
+ off = _bfd_elf_assign_file_position_for_section (hdr, off, true, 0);
elf_next_file_pos (abfd) = off;
@@ -6538,8 +6551,8 @@ assign_file_positions_for_non_load_secti
else
align = hdr->sh_addralign & -hdr->sh_addralign;
off += vma_page_aligned_bias (hdr->sh_addr, off, align);
- off = _bfd_elf_assign_file_position_for_section (hdr, off,
- false);
+ off = _bfd_elf_assign_file_position_for_section (hdr, off, false,
+ bed->s->log_file_align);
}
else if (((hdr->sh_type == SHT_REL || hdr->sh_type == SHT_RELA)
&& hdr->bfd_section == NULL)
@@ -6556,7 +6569,7 @@ assign_file_positions_for_non_load_secti
|| hdr == i_shdrpp[elf_shstrtab_sec (abfd)])
hdr->sh_offset = -1;
else
- off = _bfd_elf_assign_file_position_for_section (hdr, off, true);
+ off = _bfd_elf_assign_file_position_for_section (hdr, off, true, 0);
}
elf_next_file_pos (abfd) = off;
@@ -6793,7 +6806,8 @@ assign_file_positions_except_relocs (bfd
hdr->sh_offset = -1;
}
else
- off = _bfd_elf_assign_file_position_for_section (hdr, off, true);
+ off = _bfd_elf_assign_file_position_for_section (hdr, off, false,
+ 0);
}
elf_next_file_pos (abfd) = off;
@@ -7008,7 +7022,7 @@ _bfd_elf_assign_file_positions_for_non_l
Elf_Internal_Shdr **shdrpp, **end_shdrpp;
Elf_Internal_Shdr *shdrp;
Elf_Internal_Ehdr *i_ehdrp;
- const struct elf_backend_data *bed;
+ const struct elf_backend_data *bed = get_elf_backend_data (abfd);
/* Skip non-load sections without section header. */
if ((abfd->flags & BFD_NO_SECTION_HEADER) != 0)
@@ -7076,7 +7090,10 @@ _bfd_elf_assign_file_positions_for_non_l
sec->contents = NULL;
}
- off = _bfd_elf_assign_file_position_for_section (shdrp, off, true);
+ off = _bfd_elf_assign_file_position_for_section (shdrp, off,
+ (abfd->flags & (EXEC_P | DYNAMIC))
+ || bfd_get_format (abfd) == bfd_core,
+ bed->s->log_file_align);
}
}
@@ -7085,11 +7102,10 @@ _bfd_elf_assign_file_positions_for_non_l
_bfd_elf_strtab_finalize (elf_shstrtab (abfd));
shdrp = &elf_tdata (abfd)->shstrtab_hdr;
shdrp->sh_size = _bfd_elf_strtab_size (elf_shstrtab (abfd));
- off = _bfd_elf_assign_file_position_for_section (shdrp, off, true);
+ off = _bfd_elf_assign_file_position_for_section (shdrp, off, true, 0);
/* Place the section headers. */
i_ehdrp = elf_elfheader (abfd);
- bed = get_elf_backend_data (abfd);
off = align_file_position (off, 1 << bed->s->log_file_align);
i_ehdrp->e_shoff = off;
off += i_ehdrp->e_shnum * i_ehdrp->e_shentsize;
--- a/bfd/elf-bfd.h
+++ b/bfd/elf-bfd.h
@@ -2540,7 +2540,7 @@ extern long _bfd_elf_link_lookup_local_d
extern bool _bfd_elf_compute_section_file_positions
(bfd *, struct bfd_link_info *);
extern file_ptr _bfd_elf_assign_file_position_for_section
- (Elf_Internal_Shdr *, file_ptr, bool);
+ (Elf_Internal_Shdr *, file_ptr, bool, unsigned char);
extern bool _bfd_elf_modify_headers
(bfd *, struct bfd_link_info *);
--- a/bfd/elflink.c
+++ b/bfd/elflink.c
@@ -12914,7 +12914,7 @@ bfd_elf_final_link (bfd *abfd, struct bf
{
file_ptr off = elf_next_file_pos (abfd);
- _bfd_elf_assign_file_position_for_section (symtab_hdr, off, true);
+ _bfd_elf_assign_file_position_for_section (symtab_hdr, off, true, 0);
/* Note that at this point elf_next_file_pos (abfd) is
incorrect. We do not yet know the size of the .symtab section.
@@ -13358,7 +13358,7 @@ bfd_elf_final_link (bfd *abfd, struct bf
symtab_shndx_hdr->sh_size = amt;
off = _bfd_elf_assign_file_position_for_section (symtab_shndx_hdr,
- off, true);
+ off, true, 0);
if (bfd_seek (abfd, symtab_shndx_hdr->sh_offset, SEEK_SET) != 0
|| (bfd_write (flinfo.symshndxbuf, amt, abfd) != amt))
@@ -13382,7 +13382,7 @@ bfd_elf_final_link (bfd *abfd, struct bf
symstrtab_hdr->sh_addralign = 1;
off = _bfd_elf_assign_file_position_for_section (symstrtab_hdr,
- off, true);
+ off, true, 0);
elf_next_file_pos (abfd) = off;
if (bfd_seek (abfd, symstrtab_hdr->sh_offset, SEEK_SET) != 0
--- a/binutils/testsuite/binutils-all/i386/compressed-1b.d
+++ b/binutils/testsuite/binutils-all/i386/compressed-1b.d
@@ -10,9 +10,9 @@ There are 5 section headers, starting at
Section Headers:
\[Nr\] Name Type Addr Off Size ES Flg Lk Inf Al
\[ 0\] NULL 00000000 000000 000000 00 0 0 0
- \[ 1\] .text PROGBITS 00000000 000040 00001b 00 AX 0 0 16
- \[ 2\] .data PROGBITS 00000000 00005b 000000 00 WA 0 0 1
- \[ 3\] .bss NOBITS 00000000 00005b 000000 00 WA 0 0 1
- \[ 4\] .shstrtab STRTAB 00000000 [0-9a-f]+ 00001c 00 . 0 0 1
+ \[ 1\] .text PROGBITS 00000000 0000.. 00001b 00 AX 0 0 16
+ \[ 2\] .data PROGBITS 00000000 0000.. 000000 00 WA 0 0 1
+ \[ 3\] .bss NOBITS 00000000 0000.. 000000 00 WA 0 0 1
+ \[ 4\] .shstrtab STRTAB 00000000 0000.. 00001c 00 .. 0 0 1
Key to Flags:
#...
--- a/binutils/testsuite/binutils-all/i386/compressed-1c.d
+++ b/binutils/testsuite/binutils-all/i386/compressed-1c.d
@@ -10,9 +10,9 @@ There are 5 section headers, starting at
Section Headers:
\[Nr\] Name Type Addr Off Size ES Flg Lk Inf Al
\[ 0\] NULL 00000000 000000 000000 00 0 0 0
- \[ 1\] .text PROGBITS 00000000 000040 00001b 00 AX 0 0 16
- \[ 2\] .data PROGBITS 00000000 00005b 000000 00 WA 0 0 1
- \[ 3\] .bss NOBITS 00000000 00005b 000000 00 WA 0 0 1
- \[ 4\] .shstrtab STRTAB 00000000 [0-9a-f]+ 00001c 00 .* 0 0 1
+ \[ 1\] .text PROGBITS 00000000 0000.. 00001b 00 AX 0 0 16
+ \[ 2\] .data PROGBITS 00000000 0000.. 000000 00 WA 0 0 1
+ \[ 3\] .bss NOBITS 00000000 0000.. 000000 00 WA 0 0 1
+ \[ 4\] .shstrtab STRTAB 00000000 0000.. 00001c 00 .. 0 0 1
Key to Flags:
#...
--- a/binutils/testsuite/binutils-all/readelf.s
+++ b/binutils/testsuite/binutils-all/readelf.s
@@ -10,7 +10,7 @@ Section Headers:
# MIPS targets put .rela.text here.
#...
+\[ .\] .* +PROGBITS +00000000 0000(3c|40|44|48|50) 0000(04|10) 00 +WA +0 +0 +(.|..)
- +\[ .\] .* +NOBITS +00000000 0000(40|44|48|4c|60) 000000 00 +WA +0 +0 +(.|..)
+ +\[ .\] .* +NOBITS +00000000 0+[0-9a-f]+ 000000 00 +WA +0 +0 +(.|..)
# ARM targets put .ARM.attributes here.
# MIPS targets put .reginfo, .mdebug, .MIPS.abiflags and .gnu.attributes here.
# v850 targets put .call_table_data and .call_table_text here.
--- a/gas/testsuite/gas/aarch64/tail_padding.d
+++ b/gas/testsuite/gas/aarch64/tail_padding.d
@@ -11,10 +11,10 @@ Section Headers:
Size EntSize Flags Link Info Align
\[ 0\] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
- \[ 1\] \.text PROGBITS 0000000000000000 00000040
+ \[ 1\] \.text PROGBITS 0000000000000000 000000..
0000000000000000 0000000000000000 AX 0 0 1
- \[ 2\] \.data PROGBITS 0000000000000000 00000040
+ \[ 2\] \.data PROGBITS 0000000000000000 000000..
0000000000000008 0000000000000000 WA 0 0 64
- \[ 3\] \.bss NOBITS 0000000000000000 00000080
+ \[ 3\] \.bss NOBITS 0000000000000000 000000..
000000000000000c 0000000000000000 WA 0 0 64
#...
--- a/gas/testsuite/gas/arm/ehabi-pacbti-m.d
+++ b/gas/testsuite/gas/arm/ehabi-pacbti-m.d
@@ -4,7 +4,7 @@
#readelf: -u
#target: [is_elf_format]
-Unwind section '.ARM.exidx' at offset 0x5c contains 1 entry:
+Unwind section '.ARM.exidx' at offset 0x[0-9a-f]+ contains 1 entry:
0x0: @0x0
Compact model index: 1
--- a/gas/testsuite/gas/ia64/group-1.d
+++ b/gas/testsuite/gas/ia64/group-1.d
@@ -8,15 +8,15 @@ Section Headers:
Size EntSize Flags Link Info Align
\[ 0\] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
- \[ 1\] \.group GROUP 0000000000000000 00000040
+ \[ 1\] \.group GROUP 0000000000000000 [0-9a-f]+
0000000000000008 0000000000000004 6 6 4
- \[ 2\] \.text PROGBITS 0000000000000000 00000050
+ \[ 2\] \.text PROGBITS 0000000000000000 [0-9a-f]+
0000000000000000 0000000000000000 AX 0 0 16
- \[ 3\] \.data PROGBITS 0000000000000000 00000050
+ \[ 3\] \.data PROGBITS 0000000000000000 [0-9a-f]+
0000000000000000 0000000000000000 WA 0 0 1
- \[ 4\] \.bss NOBITS 0000000000000000 00000050
+ \[ 4\] \.bss NOBITS 0000000000000000 [0-9a-f]+
0000000000000000 0000000000000000 WA 0 0 1
- \[ 5\] \.text PROGBITS 0000000000000000 00000050
+ \[ 5\] \.text PROGBITS 0000000000000000 [0-9a-f]+
0000000000000010 0000000000000000 AXG 0 0 16
\[ 6\] \.symtab SYMTAB 0000000000000000 .*
00000000000000c0 0000000000000018 7 8 8
--- a/gas/testsuite/gas/ia64/group-2.d
+++ b/gas/testsuite/gas/ia64/group-2.d
@@ -9,19 +9,19 @@ Section Headers:
Size EntSize Flags Link Info Align
\[ 0\] NULL 0000000000000000 00000000
0000000000000000 0000000000000000 0 0 0
- \[ 1\] \.group GROUP 0000000000000000 00000040
+ \[ 1\] \.group GROUP 0000000000000000 [0-9a-f]+
0000000000000014 0000000000000004 9 5 4
- \[ 2\] \.text PROGBITS 0000000000000000 00000060
+ \[ 2\] \.text PROGBITS 0000000000000000 [0-9a-f]+
0000000000000000 0000000000000000 AX 0 0 16
- \[ 3\] \.data PROGBITS 0000000000000000 00000060
+ \[ 3\] \.data PROGBITS 0000000000000000 [0-9a-f]+
0000000000000000 0000000000000000 WA 0 0 1
- \[ 4\] \.bss NOBITS 0000000000000000 00000060
+ \[ 4\] \.bss NOBITS 0000000000000000 [0-9a-f]+
0000000000000000 0000000000000000 WA 0 0 1
- \[ 5\] \.gnu\.linkonce\.t\.f PROGBITS 0000000000000000 00000060
+ \[ 5\] \.gnu\.linkonce\.t\.f PROGBITS 0000000000000000 [0-9a-f]+
0000000000000000 0000000000000000 AXG 0 0 16
- \[ 6\] \.gnu\.linkonce\.ia6 PROGBITS 0000000000000000 00000060
+ \[ 6\] \.gnu\.linkonce\.ia6 PROGBITS 0000000000000000 [0-9a-f]+
0000000000000010 0000000000000000 AG 0 0 8
- \[ 7\] \.gnu\.linkonce\.ia6 IA_64_UNWIND 0000000000000000 00000070
+ \[ 7\] \.gnu\.linkonce\.ia6 IA_64_UNWIND 0000000000000000 [0-9a-f]+
0000000000000018 0000000000000000 ALG 5 5 8
\[ 8\] \.rela\.gnu\.linkonc RELA 0000000000000000 .*
0000000000000048 0000000000000018 IG 9 7 8
--- a/gas/testsuite/gas/mmix/bspec-2.d
+++ b/gas/testsuite/gas/mmix/bspec-2.d
@@ -1,11 +1,11 @@
#readelf: -Sr -T -x1 -x4
There are 11 section headers, starting at offset .*:
#...
- \[ 4\] \.MMIX\.spec_data\.2 PROGBITS 0+ 0+48
+ \[ 4\] \.MMIX\.spec_data\.2 PROGBITS 0+ [0-9a-f]+
0+10 0+ 0 0 8
\[ 5\] \.rela\.MMIX\.spec_d RELA 0+ .*
+0+30 0+18 +I +8 +4 +8
- \[ 6\] \.MMIX\.spec_data\.3 PROGBITS 0+ 0+58
+ \[ 6\] \.MMIX\.spec_data\.3 PROGBITS 0+ [0-9a-f]+
0+8 0+ 0 0 8
\[ 7\] \.rela\.MMIX\.spec_d RELA 0+ .*
+0+18 +0+18 +I +8 +6 +8
--- a/ld/testsuite/ld-x86-64/pr27590.rd
+++ b/ld/testsuite/ld-x86-64/pr27590.rd
@@ -1,11 +1,11 @@
#...
- \[[ 0-9]+\] .gnu.debuglto_.debug_info PROGBITS +0+ 0+28a 0+42 00 +E 0 +0 1
- \[[ 0-9]+\] .rela.gnu.debuglto_.debug_info RELA +0+ 0+810 0+f0 18 +I 26 17 8
- \[[ 0-9]+\] .gnu.debuglto_.debug_abbrev PROGBITS +0+ 0+2cc 0+26 00 +E 0 +0 1
- \[[ 0-9]+\] .gnu.debuglto_.debug_macro PROGBITS +0+ 0+2f2 0+2a 00 +E 0 +0 1
- \[[ 0-9]+\] .rela.gnu.debuglto_.debug_macro RELA +0+ 0+900 0+60 18 +I 26 20 8
- \[[ 0-9]+\] .gnu.debuglto_.debug_macro PROGBITS +0+ 0+31c 0+10 00 GE 0 +0 1
- \[[ 0-9]+\] .rela.gnu.debuglto_.debug_macro RELA +0+ 0+960 0+30 18 IG 26 22 8
- \[[ 0-9]+\] .gnu.debuglto_.debug_line PROGBITS +0+ 0+32c 0+8a 00 +E 0 +0 1
- \[[ 0-9]+\] .gnu.debuglto_.debug_str PROGBITS +0+ 0+3b6 0+15c 01 MSE 0 +0 1
+ \[[ 0-9]+\] .gnu.debuglto_.debug_info PROGBITS +0+ [0-9a-f]+ 0+42 00 +E 0 +0 1
+ \[[ 0-9]+\] .rela.gnu.debuglto_.debug_info RELA +0+ [0-9a-f]+ 0+f0 18 +I 26 17 8
+ \[[ 0-9]+\] .gnu.debuglto_.debug_abbrev PROGBITS +0+ [0-9a-f]+ 0+26 00 +E 0 +0 1
+ \[[ 0-9]+\] .gnu.debuglto_.debug_macro PROGBITS +0+ [0-9a-f]+ 0+2a 00 +E 0 +0 1
+ \[[ 0-9]+\] .rela.gnu.debuglto_.debug_macro RELA +0+ [0-9a-f]+ 0+60 18 +I 26 20 8
+ \[[ 0-9]+\] .gnu.debuglto_.debug_macro PROGBITS +0+ [0-9a-f]+ 0+10 00 GE 0 +0 1
+ \[[ 0-9]+\] .rela.gnu.debuglto_.debug_macro RELA +0+ [0-9a-f]+ 0+30 18 IG 26 22 8
+ \[[ 0-9]+\] .gnu.debuglto_.debug_line PROGBITS +0+ [0-9a-f]+ 0+8a 00 +E 0 +0 1
+ \[[ 0-9]+\] .gnu.debuglto_.debug_str PROGBITS +0+ [0-9a-f]+ 0+15c 01 MSE 0 +0 1
#pass
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