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[MC] Fix assembler infinite loop on EH table using LEB padding.

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Fix the infinite loop reported in PR35809. It can occur with GCC-style
EH table assembly, where the compiler relies on the assembler to
calculate the offsets in the EH table.

Also see https://sourceware.org/bugzilla/show_bug.cgi?id=4029 for the
equivalent issue in the GNU assembler.

Patch by Ryan Prichard!

llvm-svn: 323934
This commit is contained in:
Rafael Espindola 2018-02-01 00:25:19 +00:00
parent fd88771d7b
commit 14987cd2c8
2 changed files with 34 additions and 2 deletions
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8
lib/MC/MCAssembler.cpp
View File

@ -868,10 +868,14 @@ bool MCAssembler::relaxLEB(MCAsmLayout &Layout, MCLEBFragment &LF) {
SmallString<8> &Data = LF.getContents();
Data.clear();
raw_svector_ostream OSE(Data);
// The compiler can generate EH table assembly that is impossible to assemble
// without either adding padding to an LEB fragment or adding extra padding
// to a later alignment fragment. To accommodate such tables, relaxation can
// only increase an LEB fragment size here, not decrease it. See PR35809.
if (LF.isSigned())
encodeSLEB128(Value, OSE);
encodeSLEB128(Value, OSE, OldSize);
else
encodeULEB128(Value, OSE);
encodeULEB128(Value, OSE, OldSize);
return OldSize != LF.getContents().size();
}

28
test/MC/ELF/uleb-ehtable.s Normal file
View File

@ -0,0 +1,28 @@
// RUN: llvm-mc -filetype=obj -triple i686-pc-linux-gnu %s -o - | llvm-readobj -s -sd | FileCheck %s -check-prefix=CHECK -check-prefix=ELF
// RUN: llvm-mc -filetype=obj -triple x86_64-pc-linux-gnu %s -o - | llvm-readobj -s -sd | FileCheck %s -check-prefix=CHECK -check-prefix=ELF
// RUN: llvm-mc -filetype=obj -triple i386-apple-darwin9 %s -o - | llvm-readobj -s -sd | FileCheck %s -check-prefix=CHECK -check-prefix=MACHO
// RUN: llvm-mc -filetype=obj -triple x86_64-apple-darwin9 %s -o - | llvm-readobj -s -sd | FileCheck %s -check-prefix=CHECK -check-prefix=MACHO
// Test that we can assemble a GCC-like EH table that has 16381-16383 bytes of
// non-padding data between .ttbaseref and .ttbase. The assembler must insert
// extra padding either into the uleb128 or at the balign directive. See
// PR35809.
.data
.balign 4
foo:
.byte 0xff // LPStart omitted
.byte 0x1 // TType encoding (uleb128)
.uleb128 .ttbase-.ttbaseref
.ttbaseref:
.fill 128*128-1, 1, 0xcd // call site and actions tables
.balign 4
.ttbase:
.byte 1, 2, 3, 4
// ELF: Name: .data
// MACHO: Name: __data
// CHECK: SectionData (
// CHECK-NEXT: 0000: FF01FFFF 00CDCDCD CDCDCDCD CDCDCDCD
// CHECK: 4000: CDCDCDCD 01020304
// CHECK-NEXT: )