[Bug 269455] Using LTO on powerpc64 generates broken binaries
Date: Fri, 10 Feb 2023 09:23:29 UTC
https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=269455
Bug ID: 269455
Summary: Using LTO on powerpc64 generates broken binaries
Product: Base System
Version: CURRENT
Hardware: powerpc
OS: Any
Status: New
Severity: Affects Many People
Priority: ---
Component: bin
Assignee: bugs@FreeBSD.org
Reporter: pkubaj@FreeBSD.org
This is a repost of https://github.com/llvm/llvm-project/issues/46697.
I'm creating a PR here, because it turns out that LTO itself works fine when
using lld from ports, but is broken with the base lld (lld 15 is also
affected). It looks like it has affected powerpc64 ever since the GCC -> LLVM
switch (so LLVM 9), but I never tried linking with ports lld until now.
I have a simple test program:
int main()
{
return 0;
}
and do:
root@talos-powerpc64:~ # clang -fuse-ld=/usr/local/bin/ld.lld15 -flto test.c
root@talos-powerpc64:~ # ./a.out
root@talos-powerpc64:~ # clang -flto test.c
root@talos-powerpc64:~ # ./a.out
Segmentation fault (core dumped)
I also deassembled both binaries and did a diff:
--- baselld.S 2023-02-09 23:53:53.171611000 +0100
+++ portslld.S 2023-02-09 23:53:58.827662000 +0100
@@ -1,5 +1,5 @@
-a.out2: file format elf64-powerpc
+a.out: file format elf64-powerpc
Disassembly of section .text:
@@ -20,7 +20,7 @@
10010558: fb df 00 60 std 30, 96(31)
1001055c: 7c be 2b 78 mr 30, 5
; if (environ == NULL)
-10010560: e8 a4 80 70 ld 5, -32656(4)
+10010560: e8 a4 80 58 ld 5, -32680(4)
10010564: fb 9f 00 50 std 28, 80(31)
10010568: 28 25 00 00 cmpldi 5, 0
1001056c: 7c 7c 1b 78 mr 28, 3
@@ -33,7 +33,7 @@
; if (environ == NULL)
10010588: 40 82 00 0c bf 2, 0x10010594 <_start+0x68>
; environ = env;
-1001058c: 38 64 80 70 addi 3, 4, -32656
+1001058c: 38 64 80 58 addi 3, 4, -32680
10010590: fb c3 00 00 std 30, 0(3)
; if (argc > 0 && argv[0] != NULL) {
10010594: 2c 1c 00 01 cmpwi 28, 1
@@ -65,7 +65,7 @@
100105e0: 41 82 00 10 bt 2, 0x100105f0 <_start+0xc4>
; __ps_strings = ps_strings;
100105e4: 3c 62 00 01 addis 3, 2, 1
-100105e8: 38 63 80 68 addi 3, 3, -32664
+100105e8: 38 63 80 50 addi 3, 3, -32688
100105ec: f9 03 00 00 std 8, 0(3)
; if (&_DYNAMIC != NULL)
100105f0: 3c 62 ff ff addis 3, 2, -1
@@ -95,8 +95,8 @@
10010640: 3f 42 00 01 addis 26, 2, 1
; for (; aux->a_type != AT_NULL; aux++) {
10010644: 7c 63 f2 14 add 3, 3, 30
-10010648: 38 9b 80 78 addi 4, 27, -32648
-1001064c: 38 ba 80 7c addi 5, 26, -32644
+10010648: 38 9b 80 60 addi 4, 27, -32672
+1001064c: 38 ba 80 64 addi 5, 26, -32668
10010650: 38 63 ff f8 addi 3, 3, -8
10010654: 48 00 00 10 b 0x10010664 <_start+0x138>
10010658: 7c a7 2b 78 mr 7, 5
@@ -144,9 +144,9 @@
; target = ((ifunc_resolver_t)ptr)(cpu_features, cpu_features2,
100106e0: 7d 89 03 a6 mtctr 12
100106e4: 39 20 00 00 li 9, 0
-100106e8: 80 7b 80 78 lwz 3, -32648(27)
+100106e8: 80 7b 80 60 lwz 3, -32672(27)
100106ec: 39 40 00 00 li 10, 0
-100106f0: 80 9a 80 7c lwz 4, -32644(26)
+100106f0: 80 9a 80 64 lwz 4, -32668(26)
100106f4: 4e 80 04 21 bctrl
100106f8: e8 41 00 18 ld 2, 24(1)
; *where = target;
@@ -169,10 +169,10 @@
10010734: 4e 80 04 21 bctrl
10010738: e8 41 00 18 ld 2, 24(1)
; exit(main(argc, argv, env));
-1001073c: 3c 62 00 01 addis 3, 2, 1
+1001073c: 3c 62 ff fe addis 3, 2, -2
10010740: 7f a4 eb 78 mr 4, 29
10010744: 7f c5 f3 78 mr 5, 30
-10010748: 39 83 80 50 addi 12, 3, -32688
+10010748: 39 83 7e 30 addi 12, 3, 32304
1001074c: 7f 83 e3 78 mr 3, 28
10010750: 7d 89 03 a6 mtctr 12
10010754: 4e 80 04 21 bctrl
@@ -452,6 +452,8 @@
10010b04: eb e1 ff f8 ld 31, -8(1)
10010b08: 4e 80 00 20 blr
...
+
+0000000010010b18 <main>:
10010b18: 38 60 00 00 li 3, 0
10010b1c: 90 61 ff f4 stw 3, -12(1)
10010b20: 38 60 00 00 li 3, 0
For some reason, main function is missing when linked with the base lld.
Since this issue is non-existent with lld from ports, it must be because of how
we built LLVM. It only affects powerpc64. powerpc and powerpc64le are not
affected.
If it's necessary to have access to some powerpc64 system for debugging, I can
arrange it.
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