PR50160: we currently ignore non-PT_PHDR segments with no sections, not
accounting for its p_offset and p_filesz: this can cause an out-of-bounds write
in `writeSegmentData` if the p_offset+p_filesz is larger than the total file
size.
This can be fixed by setting p_offset=p_filesz=0. The logic nicely unifies with
the logic added in D90897.
Reviewed By: jhenderson, rupprecht
Differential Revision: https://reviews.llvm.org/D101560
We already set the `sh_entsize` field in a single place
for all non-implicit sections.
This patch reorders the logic slightly and with it
we finally have the only one place where the `sh_entsize` is set.
obj2yaml will not dump the `EntSize` key for `SHT_DYNSYM/SHT_SYMTAB` sections anymore,
when the value of `sh_entsize` is equal to `sizeof(Elf_Sym)`
Note that this also seems revealed an issue in llvm-objcopy:
Previously yaml2obj set the `sh_entsize` for the `.symtab` section to 0x18,
now we it sets it for `SHT_SYMTAB` sections, i.e. by type.
But the `llvm-objcopy/ELF/only-keep-debug.test` has a `.symtab` section of type `SHT_STRTAB`,
and now yaml2obj sets the `sh_entsize` to 0 for it.
I had to update the corresponding check lines for `ES`, but the behavior of
`llvm-objcopy` should be fixed instead I think.
I've added a TODO and a comment.
Differential revision: https://reviews.llvm.org/D95364
Alternative to D74755. sectionWithinSegment() treats an empty section as having
a size of 1. Due to the rule, an empty .tdata will not be attributed to an
empty PT_TLS. (The empty p_align=64 PT_TLS is for Android Bionic's TCB
compatibility (ELF-TLS). See https://reviews.llvm.org/D62055#1507426)
Currently --only-keep-debug will not layout a segment with no section
(layoutSegmentsForOnlyKeepDebug()), thus p_offset of PT_TLS can go past the end
of the file. The strange p_offset can trigger validation errors for subsequent
tools, e.g. llvm-objcopy errors when reading back the separate debug file
(readProgramHeaders()).
This patch places such an empty segment according to its parent segment. This
special cases works for the empty PT_TLS used in Android. For a non-empty
segment, it should have at least one non-empty section and will be handled by
the normal code. Note, p_memsz PT_LOAD is rejected by both Linux and FreeBSD.
Reviewed By: jhenderson
Differential Revision: https://reviews.llvm.org/D90897
Imagine we have a YAML declaration of few sections: `foo1`, `<unnamed 2>`, `foo3`, `foo4`.
To put them into segment we can do (1*):
```
Sections:
- Section: foo1
- Section: foo4
```
or we can use (2*):
```
Sections:
- Section: foo1
- Section: foo3
- Section: foo4
```
or (3*) :
```
Sections:
- Section: foo1
## "(index 2)" here is a name that we automatically created for a unnamed section.
- Section: (index 2)
- Section: foo3
- Section: foo4
```
It looks really confusing that we don't have to list all of sections.
At first I've tried to make this rule stricter and report an error when there is a gap
(i.e. when a section is included into segment, but not listed explicitly).
This did not work perfect, because such approach conflicts with unnamed sections/fills (see (3*)).
This patch drops "Sections" key and introduces 2 keys instead: `FirstSec` and `LastSec`.
Both are optional.
Differential revision: https://reviews.llvm.org/D90458
`PAddr` corresponds to `p_paddr` of a program header, which is the segment's physical
address for systems in which physical addressing is relevant. `p_paddr` is often equal
to `p_vaddr`, which is the virtual address of a segment.
This patch changes the default for `PAddr` from 0 to a value of `VAddr`.
Differential revision: https://reviews.llvm.org/D76131
I've noticed that it is not convenient to create YAMLs from
binaries (using obj2yaml) that have to be test cases for obj2yaml
later (after applying yaml2obj).
The problem, for example is that obj2yaml emits "DynamicSymbols:"
key instead of .dynsym. It also does not create .dynstr.
And when a YAML document without explicitly defined .dynsym/.dynstr
is given to yaml2obj, we have issues:
1) These sections are placed after non-allocatable sections (I've fixed it in D74756).
2) They have VA == 0. User needs create descriptions for such sections explicitly manually
to set a VA.
This patch addresses (2). I suggest to let yaml2obj assign virtual addresses by itself.
It makes an output binary to be much closer to "normal" ELF.
(It is still possible to use "Address: 0x0" for a section to get the original behavior
if it is needed)
Differential revision: https://reviews.llvm.org/D74764
--only-keep-debug produces a debug file as the output that only
preserves contents of sections useful for debugging purposes (the
binutils implementation preserves SHT_NOTE and non-SHF_ALLOC sections),
by changing their section types to SHT_NOBITS and rewritting file
offsets.
See https://sourceware.org/gdb/onlinedocs/gdb/Separate-Debug-Files.html
The intended use case is:
```
llvm-objcopy --only-keep-debug a a.dbg
llvm-objcopy --strip-debug a b
llvm-objcopy --add-gnu-debuglink=a.dbg b
```
The current layout algorithm is incapable of deleting contents and
shrinking segments, so it is not suitable for implementing the
functionality.
This patch adds a new algorithm which assigns sh_offset to sections
first, then modifies p_offset/p_filesz of program headers. It bears a
resemblance to lld/ELF/Writer.cpp.
Reviewed By: jhenderson, jakehehrlich
Differential Revision: https://reviews.llvm.org/D67137
Fangrui Song