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[LLD][ELF] - Disambiguate "=fillexp" with a primary expression to allow =0x90 /DISCARD/ 

Fixes https://bugs.llvm.org/show_bug.cgi?id=44903

It is about the following case:

```
SECTIONS {
  .foo : { *(.foo) } =0x90909090
  /DISCARD/ : { *(.bar) }
}
```

Here while parsing the fill expression we treated the
"/" of "/DISCARD/" as operator.

With this change, suggested by Fangrui Song, we do
not allow expressions with operators (e.g. "0x1100 + 0x22")
that are not wrapped into round brackets. It should not
be an issue for users, but helps to resolve parsing ambiguity.

Differential revision: https://reviews.llvm.org/D74687
This commit is contained in:
Georgii Rymar 2020-02-16 14:17:26 +03:00
parent 981f0802b3
commit bb7d2b1780
2 changed files with 12 additions and 4 deletions
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9
lld/ELF/ScriptParser.cpp
View File

@ -848,9 +848,9 @@ OutputSection *ScriptParser::readOutputSectionDescription(StringRef outSec) {
// We handle the FILL command as an alias for =fillexp section attribute,
// which is different from what GNU linkers do.
// https://sourceware.org/binutils/docs/ld/Output-Section-Data.html
expect("(");
if (peek() != "(")
setError("( expected, but got " + peek());
cmd->filler = readFill();
expect(")");
} else if (tok == "SORT") {
readSort();
} else if (tok == "INCLUDE") {
@ -905,8 +905,11 @@ OutputSection *ScriptParser::readOutputSectionDescription(StringRef outSec) {
// When reading a hexstring, ld.bfd handles it as a blob of arbitrary
// size, while ld.gold always handles it as a 32-bit big-endian number.
// We are compatible with ld.gold because it's easier to implement.
// Also, we require that expressions with operators must be wrapped into
// round brackets. We did it to resolve the ambiguity when parsing scripts like:
// SECTIONS { .foo : { ... } =120+3 /DISCARD/ : { ... } }
std::array<uint8_t, 4> ScriptParser::readFill() {
uint64_t value = readExpr()().val;
uint64_t value = readPrimary()().val;
if (value > UINT32_MAX)
setError("filler expression result does not fit 32-bit: 0x" +
Twine::utohexstr(value));

7
lld/test/ELF/linkerscript/sections-padding.s
View File

@ -7,7 +7,7 @@
# RUN: llvm-objdump -s %t.out | FileCheck --check-prefix=YES %s
# YES: 66000011 22000011 22000011 22000011
# RUN: echo "SECTIONS { .mysec : { *(.mysec*) } =0x1100+0x22 }" > %t.script
# RUN: echo "SECTIONS { .mysec : { *(.mysec*) } =(0x1100+0x22) }" > %t.script
# RUN: ld.lld -o %t.out --script %t.script %t
# RUN: llvm-objdump -s %t.out | FileCheck --check-prefix=YES2 %s
# YES2: 66000011 22000011 22000011 22000011
@ -66,6 +66,11 @@
# RUN: not ld.lld -o /dev/null %t --script %t.script 2>&1 | FileCheck --check-prefix=ERR4 %s
# ERR4: symbol not found: foo
## Check we are able to parse scripts where "/DISCARD/" follows a section fill expression.
# RUN: echo "SECTIONS { .mysec : { *(.mysec*) } =0x1122 /DISCARD/ : { *(.text) } }" > %t.script
# RUN: ld.lld -o %t.out --script %t.script %t
# RUN: llvm-objdump -s %t.out | FileCheck --check-prefix=YES %s
.section .mysec.1,"a"
.align 16
.byte 0x66