[llvm-bugs] [Bug 41836] New: COFF obj2yaml -> yaml2obj round trip does the wrong thing with globals in .bss
via llvm-bugs
llvm-bugs at lists.llvm.org
Fri May 10 14:05:12 PDT 2019
https://bugs.llvm.org/show_bug.cgi?id=41836
Bug ID: 41836
Summary: COFF obj2yaml -> yaml2obj round trip does the wrong
thing with globals in .bss
Product: libraries
Version: trunk
Hardware: PC
OS: Windows NT
Status: NEW
Severity: enhancement
Priority: P
Component: Object
Assignee: unassignedbugs at nondot.org
Reporter: rnk at google.com
CC: llvm-bugs at lists.llvm.org
Seems related to https://bugs.llvm.org/show_bug.cgi?id=8338
Specifically, SizeOfRawData for .bss sections is not preserved, it is zeroed
out. LLD currently contains a lot of yaml input test cases with accidentally
zero-sized globals in .bss because of this.
Consider:
$ cat bss.s
.bss
.global gv_bss
gv_bss:
.long 0
$ llvm-mc bss.s -o bss.obj -filetype=obj
$ obj2yaml bss.obj | yaml2obj -o bss2.obj
$ llvm-readobj -sections bss.obj > bss1.txt
$ llvm-readobj -sections bss2.obj > bss2.txt
$ diff -u bss1.txt bss2.txt
--- bss1.txt 2019-05-10 14:00:19.121866800 -0700
+++ bss2.txt 2019-05-10 14:00:22.056197400 -0700
@@ -1,5 +1,5 @@
-File: bss.obj
+File: bss2.obj
Format: COFF-x86-64
Arch: x86_64
AddressSize: 64bit
@@ -10,7 +10,7 @@
VirtualSize: 0x0
VirtualAddress: 0x0
RawDataSize: 0
- PointerToRawData: 0x8C
+ PointerToRawData: 0x0
PointerToRelocations: 0x0
PointerToLineNumbers: 0x0
RelocationCount: 0
@@ -28,7 +28,7 @@
VirtualSize: 0x0
VirtualAddress: 0x0
RawDataSize: 0
- PointerToRawData: 0x8C
+ PointerToRawData: 0x0
PointerToRelocations: 0x0
PointerToLineNumbers: 0x0
RelocationCount: 0
@@ -45,7 +45,7 @@
Name: .bss (2E 62 73 73 00 00 00 00)
VirtualSize: 0x0
VirtualAddress: 0x0
- RawDataSize: 4
+ RawDataSize: 0
PointerToRawData: 0x0
PointerToRelocations: 0x0
PointerToLineNumbers: 0x0
The .data and .text differences are mostly meaningless, I think. Reducing the
size of the .bss section is an issue because it changes the meaning of the
object pretty significantly: globals in .bss get smaller.
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