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[PATCH] Ignore sh_offset of NOBITS sections
Hi,
Consider a hello world with debug info. If we split off the debug info using
objcopy, we run into the following dwz failure:
...
$ gcc hello.c -g
$ objcopy --only-keep-debug a.out a.debug
$ dwz a.debug
dwz: Allocatable section in a.debug after non-allocatable ones
...
Dwz is complaining about section 19, which has an sh_offset of 0xe00:
...
[19] .init_array NOBITS 0000000000600e00 00000e00
0000000000000008 0000000000000008 WA 0 0 8
...
which is larger than the sh_offset of 0x410 of section 28:
...
[28] .debug_info PROGBITS 0000000000000000 00000410
00000000000005bb 0000000000000000 0 0 1...
...
However, the sh_offset field is meaningless for NOBITS sections, so the error
is unnecessary.
Fix the error by ignoring NOBITS sections in write_dso when:
- sanity-checking the section header table, and
- updating the offsets of sections and section header table to honour
required aligmment.
In order to ensure that the sanity-checking of the section header table is not
too much weakened by skipping the NOBITS sections, add verify_alloc_sections,
which checks that:
- there are no allocatable sections after non-allocatable ones
(after in terms of section header table order)
- the allocatable sections in the section header table are monotonically
increasing in sh_addr
- the allocatable sections in the section header table are monotonically
increasing in sh_offset (this is not guaranteed for NOBITS sections, but
seems to be respected by objcopy --only-keep-debug).
Finally, ensure that sh_offset for NOBITS sections are unmodified by dwz,
which seems a more sane approach than trying to update values that are
potentially undefined.
OK for trunk?
Thanks,
- Tom
Ignore sh_offset of NOBITS sections
2019-03-12 Tom de Vries <tdevries@suse.de>
PR dwz/24251
* dwz.c (verify_alloc_sections): New function.
(write_dso): Ignore sh_offset of NOBITS sections.
* testsuite/dwz.tests/objcopy-eu-unstrip-multifile.sh: New test.
* testsuite/dwz.tests/objcopy-eu-unstrip.sh: New test.
---
dwz.c | 76 +++++++++++++++++++++-
.../dwz.tests/objcopy-eu-unstrip-multifile.sh | 24 +++++++
testsuite/dwz.tests/objcopy-eu-unstrip.sh | 20 ++++++
3 files changed, 118 insertions(+), 2 deletions(-)
diff --git a/dwz.c b/dwz.c
index 476807a..dffab77 100644
--- a/dwz.c
+++ b/dwz.c
@@ -9968,6 +9968,57 @@ read_dwarf (DSO *dso, bool quieter)
return read_debug_info (dso, DEBUG_INFO);
}
+/* Verify properties of SHF_ALLOC sections in the section header table. */
+static int
+verify_alloc_sections (DSO *dso)
+{
+ int i;
+ int prev_alloc, update_prev_alloc;
+
+ prev_alloc = -1;
+ for (i = 1; i < dso->ehdr.e_shnum; ++i, prev_alloc = update_prev_alloc)
+ {
+ update_prev_alloc = prev_alloc;
+ if ((dso->shdr[i].sh_flags & SHF_ALLOC) == 0)
+ continue;
+ update_prev_alloc = i;
+
+ if (/* First allocatable section is not first section. */
+ (prev_alloc == -1 && i != 1)
+ /* Previous allocatable section is not immediately preceding
+ section. */
+ || (prev_alloc != -1 && prev_alloc != i - 1))
+ {
+ error (0, 0, "Allocatable section in %s after non-allocatable "
+ "ones", dso->filename);
+ return 1;
+ }
+
+ if (prev_alloc == -1)
+ continue;
+
+ if (!(dso->shdr[prev_alloc].sh_addr <= dso->shdr[i].sh_addr))
+ {
+ error (0, 0, "Allocatable sections in %s not monotonically "
+ "increasing in sh_addr", dso->filename);
+ return 1;
+ }
+
+ /* Even if sh_offset has no meaning for NOBITS sections, objcopy
+ --only-keep-debug seems to generate monotonically increasing sh_offset
+ for allocatable sections, so don't exclude NOBITS sections from the
+ verification here. */
+ if (!(dso->shdr[prev_alloc].sh_offset <= dso->shdr[i].sh_offset))
+ {
+ error (0, 0, "Allocatable sections in %s not monotonically "
+ "increasing in sh_offset", dso->filename);
+ return 1;
+ }
+ }
+
+ return 0;
+}
+
/* Open an ELF file NAME. */
static DSO *
fdopen_dso (int fd, const char *name)
@@ -10056,6 +10107,10 @@ write_dso (DSO *dso, const char *file, struct stat *st)
GElf_Word shstrtabadd = 0;
char *shstrtab = NULL;
bool remove_sections[SECTION_COUNT];
+ GElf_Off old_sh_offset[dso->ehdr.e_shnum];
+
+ for (i = 1; i < dso->ehdr.e_shnum; ++i)
+ old_sh_offset[i] = dso->shdr[i].sh_offset;
memset (remove_sections, '\0', sizeof (remove_sections));
ehdr = dso->ehdr;
@@ -10146,11 +10201,21 @@ write_dso (DSO *dso, const char *file, struct stat *st)
}
}
+ /* The value of sh_offset for NOBITS sections is meaningless. Reset to the
+ original value. */
+ for (i = 1; i < dso->ehdr.e_shnum; ++i)
+ if (dso->shdr[i].sh_type == SHT_NOBITS)
+ dso->shdr[i].sh_offset = old_sh_offset[i];
+
+ if (verify_alloc_sections (dso))
+ return 1;
+
if (min_shoff != ~(GElf_Off) 0)
{
for (j = 1; j < dso->ehdr.e_shnum; ++j)
if (dso->shdr[j].sh_offset >= min_shoff
&& dso->shdr[j].sh_addralign > 1
+ && dso->shdr[j].sh_type != SHT_NOBITS
&& (dso->shdr[j].sh_offset & (dso->shdr[j].sh_addralign - 1)) != 0)
break;
if (j < dso->ehdr.e_shnum
@@ -10166,10 +10231,11 @@ write_dso (DSO *dso, const char *file, struct stat *st)
for (j = 1; j < dso->ehdr.e_shnum; ++j)
if (dso->shdr[j].sh_offset < min_shoff && !last_shoff)
continue;
+ else if (dso->shdr[j].sh_type == SHT_NOBITS)
+ continue;
else if ((dso->shdr[j].sh_flags & SHF_ALLOC) != 0)
{
- error (0, 0, "Allocatable section in %s after non-allocatable "
- "ones", dso->filename);
+ error (0, 0, "Can't update allocatable section in %s", dso->filename);
return 1;
}
else if (dso->shdr[j].sh_offset < last_shoff)
@@ -10201,6 +10267,8 @@ write_dso (DSO *dso, const char *file, struct stat *st)
}
if (j == dso->ehdr.e_shnum)
break;
+ if (dso->shdr[j].sh_type == SHT_NOBITS)
+ continue;
dso->shdr[j].sh_offset = last_shoff;
if (dso->shdr[j].sh_addralign > 1)
dso->shdr[j].sh_offset
@@ -10213,6 +10281,10 @@ write_dso (DSO *dso, const char *file, struct stat *st)
}
}
+ for (i = 1; i < dso->ehdr.e_shnum; ++i)
+ if (dso->shdr[i].sh_type == SHT_NOBITS)
+ assert (dso->shdr[i].sh_offset == old_sh_offset[i]);
+
if (shstrtabadd != 0)
{
shstrtab = (char *) malloc (dso->shdr[dso->ehdr.e_shstrndx].sh_size);
diff --git a/testsuite/dwz.tests/objcopy-eu-unstrip-multifile.sh b/testsuite/dwz.tests/objcopy-eu-unstrip-multifile.sh
new file mode 100755
index 0000000..03ab852
--- /dev/null
+++ b/testsuite/dwz.tests/objcopy-eu-unstrip-multifile.sh
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+set -e
+
+cp ../hello 1
+
+objcopy --only-keep-debug 1 1.debug
+objcopy --strip-debug 1 1.stripped
+
+cp 1.debug 2.debug
+
+dwz -m 3 1.debug 2.debug
+
+rm 2.debug
+
+eu-unstrip 1.stripped 1.debug -o 1.unstripped
+
+smaller-than.sh 1.unstripped 1
+
+ls=$(ls)
+ls=$(echo $ls)
+[ "$ls" = "1 1.debug 1.stripped 1.unstripped 3" ]
+
+rm -f 1 1.debugged 1.stripped 1.unstripped 3
diff --git a/testsuite/dwz.tests/objcopy-eu-unstrip.sh b/testsuite/dwz.tests/objcopy-eu-unstrip.sh
new file mode 100755
index 0000000..9fbb5cc
--- /dev/null
+++ b/testsuite/dwz.tests/objcopy-eu-unstrip.sh
@@ -0,0 +1,20 @@
+#!/bin/sh
+
+set -e
+
+cp ../hello 1
+
+objcopy --only-keep-debug 1 1.debug
+objcopy --strip-debug 1 1.stripped
+
+dwz 1.debug
+
+eu-unstrip 1.stripped 1.debug -o 1.unstripped
+
+smaller-than.sh 1.unstripped 1
+
+ls=$(ls)
+ls=$(echo $ls)
+[ "$ls" = "1 1.debug 1.stripped 1.unstripped" ]
+
+rm -f 1 1.debugged 1.stripped 1.unstripped