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[lld][WebAssembly] Fix non-pie dynamic-linking executable #108146

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Merged
merged 8 commits into from
Jan 3, 2025
Merged

[lld][WebAssembly] Fix non-pie dynamic-linking executable #108146

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82a12e6
[lld][WebAssembly] Fix non-pie dynamic-linking executable
yamt Sep 19, 2024
06482d7
add a test
yamt Oct 1, 2024
fb9a6ab
dylink-non-pie.s: use the existing file
yamt Oct 1, 2024
9e234c1
tweak the order of conditions
yamt Oct 1, 2024
972b540
lld/test/wasm/dylink-non-pie.s: simplify
yamt Oct 1, 2024
9c486a4
lld/test/wasm/dylink-non-pie.s: check the contents of __wasm_apply_da…
yamt Oct 2, 2024
35ecf24
lld/test/wasm/dylink-non-pie.s: ensure it doesn't import __memory_base
yamt Oct 2, 2024
156e6f2
lld/test/wasm/dylink-non-pie.s: remove a few unnecessary things
yamt Nov 1, 2024
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6 changes: 6 additions & 0 deletions lld/test/wasm/Inputs/lib.s
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@@ -0,0 +1,6 @@
.functype f () -> ()
.globl f
.type f,@function
f:
.functype f () -> ()
end_function
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@sbc100 sbc100 Oct 1, 2024

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Rather than creating a new file here you can just pick an existing file such as ret32.s and compile that

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@yamt yamt Oct 1, 2024

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ok. i will try.

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@yamt yamt Oct 1, 2024

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done

35 changes: 35 additions & 0 deletions lld/test/wasm/dylink-non-pie.s
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@@ -0,0 +1,35 @@
# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.lib.o %p/Inputs/lib.s
# RUN: wasm-ld -m wasm32 --experimental-pic -shared --no-entry %t.lib.o -o %t.lib.so
# RUN: llvm-mc -filetype=obj -mattr=+reference-types -triple=wasm32-unknown-unknown -o %t.o %s
# RUN: wasm-ld -m wasm32 --features=mutable-globals -Bdynamic --export-table --growable-table --export-memory --export=__stack_pointer --export=__heap_base --export=__heap_end --entry=_start %t.o %t.lib.so -o %t.wasm
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@sbc100 sbc100 Oct 1, 2024

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Can you remove any link flags that you don't need here? e.g. all of the --export flags and the --entry flag?

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@yamt yamt Oct 1, 2024

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i wanted to mimic the real situation to link a non-pie executable.

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@yamt yamt Oct 1, 2024

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done

# RUN: obj2yaml %t.wasm | FileCheck %s

.tabletype __indirect_function_table, funcref
.globaltype __memory_base, i32, immutable

.functype f () -> ()
.functype _start () -> ()
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@sbc100 sbc100 Oct 31, 2024

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This line is not needed since its already on line 13

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@yamt yamt Nov 1, 2024

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removed

.globl _start
.type _start,@function
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@sbc100 sbc100 Oct 31, 2024

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this line is not needed I think

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@yamt yamt Nov 1, 2024

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removed

_start:
.functype _start () -> ()
global.get __memory_base
i32.const f_p@MBREL
i32.add
i32.load 0
call_indirect __indirect_function_table, () -> ()
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@sbc100 sbc100 Oct 1, 2024

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You don't need the __indirect_function_table symbol to make this test work. You can just do i32.const f_p followed by drop I think.

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@yamt yamt Oct 1, 2024

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let me think a bit. thank you.

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@yamt yamt Oct 1, 2024

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done

end_function

.section .data.f_p,"",@
.globl f_p
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@sbc100 sbc100 Oct 31, 2024

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Does this need to be global symbol? i.e. can you remove this line?

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@yamt yamt Nov 1, 2024

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it doesn't seem necessary. removed. thank you.

f_p:
.int32 f
.size f_p, 4

# CHECK: Sections:
# CHECK-NEXT: - Type: CUSTOM
# CHECK-NEXT: Name: dylink.0

# CHECK: - Type: EXPORT
# CHECK: - Name: __wasm_apply_data_relocs
# CHECK-NEXT: Kind: FUNCTION
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@sbc100 sbc100 Oct 1, 2024

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Should we be checking for some more things here?

Perhaps we can check that GOT.ret32 is imported? Perhaps we can decompile __wasm_apply_data_relocs and verify that is using GOT.ret32 as expected?

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@yamt yamt Oct 1, 2024

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do you know any existing tests doing similar things which i can use as an example?

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@sbc100 sbc100 Oct 1, 2024

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Yes, there are a few tests that disassembly stuff. Looks for DIS-NEXT in lld/test/wasm.

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@yamt yamt Oct 1, 2024

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ok. i will take a look.

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@yamt yamt Oct 2, 2024

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done

3 changes: 2 additions & 1 deletion lld/wasm/Relocations.cpp
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Expand Up @@ -146,7 +146,8 @@ void scanRelocations(InputChunk *chunk) {

if (ctx.isPic ||
(sym->isUndefined() &&
config->unresolvedSymbols == UnresolvedPolicy::ImportDynamic)) {
config->unresolvedSymbols == UnresolvedPolicy::ImportDynamic) ||
sym->isShared()) {
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@sbc100 sbc100 Oct 1, 2024

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Can you put this new clause on line 147 (e.g. if (ctx.isPic || sym->isShared() ||)

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@yamt yamt Oct 1, 2024

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ok

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@yamt yamt Oct 1, 2024

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done

switch (reloc.Type) {
case R_WASM_TABLE_INDEX_SLEB:
case R_WASM_TABLE_INDEX_SLEB64:
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