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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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38 changes: 38 additions & 0 deletions lld/test/wasm/dylink-non-pie.s
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Original file line number Diff line number Diff line change
@@ -0,0 +1,38 @@
# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.lib.o %p/Inputs/ret32.s
# RUN: wasm-ld -m wasm32 --experimental-pic -shared --no-entry %t.lib.o -o %t.lib.so
# RUN: llvm-mc -filetype=obj -triple=wasm32-unknown-unknown -o %t.o %s
# RUN: wasm-ld -m wasm32 -Bdynamic %t.o %t.lib.so -o %t.wasm
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@sbc100 sbc100 Oct 1, 2024

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Just to confirm, this effectively generates a non-PIC output? And ctx.isPic not set?

I wonder if we can confirm this this test somehow? Perhaps its enough that we successfully use i32.const f_p (which would not work if the output was PIC, right?) instead of i32.const f_p@MBREL

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@yamt yamt Oct 1, 2024

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ctx.isPic is not set as neither of pie or shared is set.

the following is the generated output. it looks reasonable to me.

(module $dylink-non-pie.s.tmp.wasm
  (type (;0;) (func (param f32) (result i32)))
  (type (;1;) (func))
  (import "env" "ret32" (func $ret32 (type 0)))
  (import "GOT.func" "ret32" (global $ret32 (mut i32)))
  (func $__wasm_apply_data_relocs (type 1)
    i32.const 1024
    global.get $ret32
    i32.store)
  (func $_start (type 1)
    i32.const 1024
    drop)
  (table (;0;) 1 1 funcref)
  (memory (;0;) 2)
  (global $__stack_pointer (mut i32) (i32.const 66576))
  (export "memory" (memory 0))
  (export "_start" (func $_start))
  (export "__wasm_apply_data_relocs" (func $__wasm_apply_data_relocs))
  (data $.data (i32.const 1024) "\00\00\00\00"))

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@yamt yamt Oct 1, 2024

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I wonder if we can confirm this this test somehow? Perhaps its enough that we successfully use i32.const f_p (which would not work if the output was PIC, right?) instead of i32.const f_p@MBREL

maybe we can confirm it doesn't have __memory_base/__table_base imports?

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@yamt yamt Oct 2, 2024

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done

# RUN: obj2yaml %t.wasm | FileCheck %s
# RUN: llvm-objdump -d --no-show-raw-insn --no-leading-addr %t.wasm | FileCheck %s --check-prefixes DIS

.functype ret32 (f32) -> (i32)
.globl _start
_start:
.functype _start () -> ()
i32.const f_p
drop
end_function

.section .data.f_p,"",@
f_p:
.int32 ret32
.size f_p, 4

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

# non-pie executable doesn't import __memory_base
# CHECK: - Type: IMPORT
# CHECK-NOT: Field: __memory_base

# 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


# DIS: <__wasm_apply_data_relocs>:
# DIS-EMPTY:
# DIS-NEXT: i32.const 1024
# DIS-NEXT: global.get 0
# DIS-NEXT: i32.store 0
# DIS-NEXT: end
2 changes: 1 addition & 1 deletion lld/wasm/Relocations.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -144,7 +144,7 @@ void scanRelocations(InputChunk *chunk) {
break;
}

if (ctx.isPic ||
if (ctx.isPic || sym->isShared() ||
(sym->isUndefined() &&
config->unresolvedSymbols == UnresolvedPolicy::ImportDynamic)) {
switch (reloc.Type) {
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