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[ELF] --oformat=binary: use LMA to compute file offsets

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--oformat=binary is rare (used in a few places in FreeBSD, see `stand/i386/mbr/Makefile` `LDFLAGS_BIN`)
The result should be identical to a normal output transformed by `objcopy -O binary`.

The current implementation ignores addresses and lays out sections by
respecting output section alignments. It can fail when an output section
address is specified, e.g. `.rodata ALIGN(16) :` (PR33651).

Fix PR33651 by respecting LMA. The code is similar to
`tools/llvm-objcop/ELF/Object.cpp` BinaryWriter::finalize after D71035 and D79229.
Unforunately for an output section without PT_LOAD, we assume its LMA is equal
to its VMA. So the result is still incorrect when an output section LMA
(`AT(...)`) is specified

Also drop `alignTo(off, config->wordsize)`. GNU ld does not round up the file size.

Differential Revision: https://reviews.llvm.org/D85086
This commit is contained in:
Fangrui Song 2020-08-05 09:04:56 -07:00
parent 98d91aecb2
commit acb66b9111
3 changed files with 46 additions and 9 deletions
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21
lld/ELF/Writer.cpp
View File

@ -2547,11 +2547,24 @@ static uint64_t setFileOffset(OutputSection *os, uint64_t off) {
}
template <class ELFT> void Writer<ELFT>::assignFileOffsetsBinary() {
uint64_t off = 0;
// Compute the minimum LMA of all non-empty non-NOBITS sections as minAddr.
auto needsOffset = [](OutputSection &sec) {
return sec.type != SHT_NOBITS && (sec.flags & SHF_ALLOC) && sec.size > 0;
};
uint64_t minAddr = UINT64_MAX;
for (OutputSection *sec : outputSections)
if (sec->flags & SHF_ALLOC)
off = setFileOffset(sec, off);
fileSize = alignTo(off, config->wordsize);
if (needsOffset(*sec)) {
sec->offset = sec->getLMA();
minAddr = std::min(minAddr, sec->offset);
}
// Sections are laid out at LMA minus minAddr.
fileSize = 0;
for (OutputSection *sec : outputSections)
if (needsOffset(*sec)) {
sec->offset -= minAddr;
fileSize = std::max(fileSize, sec->offset + sec->size);
}
}
static std::string rangeToString(uint64_t addr, uint64_t len) {

5
lld/test/ELF/oformat-binary-ttext.s
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@ -4,9 +4,8 @@
# RUN: ld.lld -N -Ttext 0x100 -o %t.out %t --oformat binary
# RUN: od -t x1 -v %t.out | FileCheck %s --check-prefix=BIN
# BIN: 0000000 90 00 00 00 00 00 00 00
# BIN-NEXT: 0000010
# BIN-NOT: 0000020
# BIN: 0000000 90
# BIN-NEXT: 0000001
## The same but without OMAGIC.
# RUN: ld.lld -Ttext 0x100 -o %t.out %t --oformat binary

29
lld/test/ELF/oformat-binary.s
View File

@ -3,8 +3,8 @@
# RUN: ld.lld -o %t.out %t --oformat binary
# RUN: od -t x1 -v %t.out | FileCheck %s
# CHECK: 000000 90 11 22 00 00 00 00 00
# CHECK-NOT: 00000010
# CHECK: 0000000 90 11 22
# CHECK-NEXT: 0000003
## Check case when linkerscript is used.
# RUN: echo "SECTIONS { . = 0x1000; }" > %t.script
@ -15,6 +15,31 @@
# RUN: ld.lld -o %t2.out --script %t.script %t --oformat binary
# RUN: od -t x1 -v %t2.out | FileCheck %s
## LMA(.text)=0x100, LMA(.mysec)=0x108. The minimum LMA of all non-empty sections is 0x100.
## We place an output section at its LMA minus 0x100.
# RUN: echo 'SECTIONS { .text 0x100 : {*(.text)} .mysec ALIGN(8) : {*(.mysec*)} }' > %talign.lds
# RUN: ld.lld -T %talign.lds %t --oformat binary -o %talign
# RUN: od -Ax -t x1 %talign | FileCheck %s --check-prefix=ALIGN --ignore-case
# ALIGN: 000000 90 00 00 00 00 00 00 00 11 22
# ALIGN-NEXT: 00000a
## The empty section .data is ignored when computing the file size.
# RUN: echo 'SECTIONS { .text : {*(.text .mysec*)} .data 0x100 : {keep = .;}}' > %tempty.lds
# RUN: ld.lld -T %tempty.lds %t --oformat binary -o %tempty
# RUN: od -t x1 %tempty | FileCheck %s
## NOBITS sections are ignored as well.
# RUN: echo 'SECTIONS { .text : {*(.text .mysec*)} .data 0x100 (NOLOAD) : {BYTE(0)}}' > %tnobits.lds
# RUN: ld.lld -T %tnobits.lds %t --oformat binary -o %tnobits
# RUN: od -t x1 %tnobits | FileCheck %s
## FIXME .mysec should be placed at file offset 1.
## This does not work because for a section without PT_LOAD, we consider LMA = VMA.
# RUN: echo 'SECTIONS { .text : {*(.text)} .mysec 0x8 : AT(1) {*(.mysec*)} }' > %tlma.lds
# RUN: ld.lld -T %tlma.lds %t --oformat binary -o %tlma
# RUN: od -Ax -t x1 %tlma | FileCheck %s --check-prefix=ALIGN --ignore-case
# RUN: not ld.lld -o /dev/null %t --oformat foo 2>&1 \
# RUN: | FileCheck %s --check-prefix ERR
# ERR: unknown --oformat value: foo