<table border="1" cellspacing="0" cellpadding="8">
<tr>
<th>Issue</th>
<td>
<a href=https://github.com/llvm/llvm-project/issues/63811>63811</a>
</td>
</tr>
<tr>
<th>Summary</th>
<td>
LLVM ERROR: malformed uleb128, extends past end (lld, wasm module asm, Windows)
</td>
</tr>
<tr>
<th>Labels</th>
<td>
new issue
</td>
</tr>
<tr>
<th>Assignees</th>
<td>
</td>
</tr>
<tr>
<th>Reporter</th>
<td>
CAD97
</td>
</tr>
</table>
<pre>
I triggered this from Rust so the minimized repro is in Rust; I don't know how to get this into clang/llvm terms on Windows. Asking rustc to emit `.ll`, `.s`, or `.bc` doesn't hit the error, so this is probably a code generator issue, IIUC. I've also provided the `.ll` and `.s`, but couldn't find the entry points to reproduce from those (the rust distribution exposes a rust-lld but not a rust-llc, as far as I can tell).
<details><summary>Version info</summary>
```text
$ rustc -Vv
rustc 1.73.0-nightly (8ca44ef9c 2023-07-10)
binary: rustc
commit-hash: 8ca44ef9caa4049d584fbbce218c219cdca33a2f
commit-date: 2023-07-10
host: x86_64-pc-windows-msvc
release: 1.73.0-nightly
LLVM version: 16.0.5
$ rust-lld -flavor wasm --version --verbose
LLD 16.0.5
```
-----
</details>
<details><summary>Rust reproduction</summary>
```rust
#![feature(asm_experimental_arch)]
#![no_std]
core::arch::global_asm! {
r#"
.section .text.make_answer,"",@
.globl make_answer
.type make_answer,@function
make_answer:
end_function
"#,
}
#[panic_handler]
fn panic(_info: &core::panic::PanicInfo) -> ! {
loop {}
}
```
Compile with `rustc --edition=2021 src\lib.rs --crate-type=cdylib --target wasm32-unknown-unknown`.
-----
</details>
<details><summary>LLVM-IR</summary>
Add `--emit=llvm-ir` to the `rustc` invocation to generate a `.ll` file. This step does not result in any errors.
```rust
; ModuleID = 'lib.ade653b175f4ee81-cgu.0'
source_filename = "lib.ade653b175f4ee81-cgu.0"
target datalayout = "e-m:e-p:32:32-p10:8:8-p20:8:8-i64:64-n32:64-S128-ni:1:10:20"
target triple = "wasm32-unknown-unknown"
module asm ""
module asm " .section .text.make_answer,\22\22,@"
module asm " .globl make_answer"
module asm " .type make_answer,@function"
module asm " make_answer:"
module asm " end_function"
module asm " "
; Function Attrs: noreturn nounwind
define hidden void @rust_begin_unwind(ptr align 4 %_info) unnamed_addr #0 {
start:
br label %bb1
bb1: ; preds = %bb1, %start
br label %bb1
}
attributes #0 = { noreturn nounwind "target-cpu"="generic" }
```
-----
</details>
<details><summary>asm</summary>
Similarly, `--emit=asm` stops compilation before the error occurs.
```asm
.text
.file "lib.ade653b175f4ee81-cgu.0"
.section .text.make_answer,"",@
.globl make_answer
make_answer:
end_function
.tabletype __indirect_function_table, funcref
.functype rust_begin_unwind (i32) -> ()
.section .text.rust_begin_unwind,"",@
.hidden rust_begin_unwind
.globl rust_begin_unwind
.type rust_begin_unwind,@function
rust_begin_unwind:
.functype rust_begin_unwind (i32) -> ()
.LBB0_1:
loop
br 0
.LBB0_2:
end_loop
end_function
.section .custom_section.target_features,"",@
.int8 2
.int8 43
.int8 15
.ascii "mutable-globals"
.int8 43
.int8 8
.ascii "sign-ext"
.section .text.rust_begin_unwind,"",@
```
It looks like perhaps the `.type` didn't make it through translation?
-----
</details>
<details><summary>LLD error</summary>
Unfortunately I wasn't able to find the tool to provide `.ll` directly to on Windows (the rust distribution provides a `rust-lld` but not a `rust-llc`), so reproduction uses the `.o` produced by the previous `rustc` invocation. None of the `-L` arguments provided by rustc are actually needed for this reproduction, so this copy of the error is generated without them.
```text
LLVM ERROR: malformed uleb128, extends past end
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
Stack dump:
0. Program arguments: D:\\.rust\\rustup\\toolchains\\nightly-x86_64-pc-windows-msvc\\lib\\rustlib\\x86_64-pc-windows-msvc\\bin\\rust-lld.exe -flavor wasm --rsp-quoting=posix --export=__heap_base --export=__data_end -z stack-size=1048576 --stack-first --allow-undefined --fatal-warnings --no-demangle --no-entry lib.lib.ade653b175f4ee81-cgu.0.rcgu.o -o lib.wasm --gc-sections --no-entry -O0
Exception Code: 0xC000001D
#0 0x00007ff6afbdf9c6 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x1aff9c6)
#1 0x00007ff6afb8ef5e (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x1aaef5e)
#2 0x00007ff6afb8f194 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x1aaf194)
#3 0x00007ff6afbe6a9a (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x1b06a9a)
#4 0x00007ff6afbe6944 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x1b06944)
#5 0x00007ff6b061ae78 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x253ae78)
#6 0x00007ff6b0615e48 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x2535e48)
#7 0x00007ff6b0613ff0 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x2533ff0)
#8 0x00007ff6b0613943 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x2533943)
#9 0x00007ff6b06135b5 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x25335b5)
#10 0x00007ff6af60051e (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x152051e)
#11 0x00007ff6af602131 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x1522131)
#12 0x00007ff6af5fae5e (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x151ae5e)
#13 0x00007ff6ae3e2792 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x302792)
#14 0x00007ff6ae3d4b98 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x2f4b98)
#15 0x00007ff6ae3d08ea (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x2f08ea)
#16 0x00007ff6ae3cce50 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x2ece50)
#17 0x00007ff6ae0e1cac (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x1cac)
#18 0x00007ff6ae0e1438 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x1438)
#19 0x00007ff6afb7b3b8 (D:\.rust\rustup\toolchains\nightly-x86_64-pc-windows-msvc\lib\rustlib\x86_64-pc-windows-msvc\bin\rust-lld.exe+0x1a9b3b8)
#20 0x00007fff12f626ad (C:\WINDOWS\System32\KERNEL32.DLL+0x126ad)
#21 0x00007fff13f8aa68 (C:\WINDOWS\SYSTEM32\ntdll.dll+0x5aa68)
```
-----
</details>
Rust sets the flag to make `llvm_unreachable` generate `trap`, and the exit code is STATUS_ILLEGAL_INSTRUCTION, so the error probably comes from one of those.
<details><summary>Variations</summary>
Module level asm of
```asm
.section .text.make_answer,"",@
.globl make_answer
.type make_answer,@function
make_answer:
end_function
```
is causing a crash with STATUS_ILLEGAL_INSTRUCTION, printing LLVM ERROR: malformed uleb128, extends past end;
```asm
.section .text.make_answer,"",@
.globl make_answer
.type make_answer,@function
make_answer:
.functype make_answer () -> ()
end_function
```
causes a silent crash due to STATUS_ACCESS_VIOLATION without printing anything; and
```asm
.functype make_answer () -> ()
.section .text.make_answer,"",@
.globl make_answer
.type make_answer,@function
make_answer:
.functype make_answer () -> ()
end_function
```
compiles without crashing... sometimes. It seems essentially random whether this crashes or not.
-----
</details>
XY: I'm attempting to play around with defining `externref`-speaking functions directly, without using a post-processing step. I built the GAS syntax by looking at `--emit=asm` and mirroring what was done there; as such there's likely all sorts of "you're holding it wrong" in how I was trying to do things. But LLVM still shouldn't be crashing. There's [other](https://github.com/llvm/llvm-project/commit/ef7ca14) cases of wasm codegen reaching `llvm_unreachable` getting fixed; this is likely another one of those.
I would try to reproduce with trunk llc on godbolt compiler explorer, but if it's possible to get it to do the codegen step, I don't know how.
</pre>
<img width="1px" height="1px" alt="" src="http://email.email.llvm.org/o/eJzcWklz47iS_jXwJYMKEhS1HHyQJfuFYtxVHeXq7nknBUgmJUyBAAcAbat__USC1EJvtbw-KEZhSySITH7IRC5IQDgntxrxmmU3LFtdidbvjL1eLlbz6VVuyv31GryV2y1aLMHvpIPKmhq-tM6DM-B3CLXUspZ_YwkWG2tAOpA69GDpDayhNJrxqYdv2jzBzjyBN7BF33GT2hsolNBbxu-UeqzBo60dGA1_SV2aJzeChfsm9RZs63xBxFhLD2wSj5Rik5jxZbhx_bWx4TYv2CSG0qDr3r6TPqBFa42lfgE9IXDQWJOLXO1BQGFKhC1qtMIbC9K5Fqn3ev3HcgRrxqePCEI5Q0SPsgxSwRMaELocwMlbD4VpVdnBqKTuKFB7u4fGSO0dDSrIrmwL7ATsd8YhMD6jvjRyKKXzVuatl0YDPjfGoQMRnkVKleFF2vhTU0GvFw4qYelnDYXQ4FEpxucjFq9YvOi_02WJXkjlWHrL0qVr61rYPUtv_0Tr6HVSV4alS8bvTs8GHCZx9-fx2fdNfNxrLPrzsWvqbpPRNB3FkZbbnVd7GuKsEOMxVvMCeMzTKJ5GScz4vCPKpQ7vW3TcusbC1LX00U64HT05MhBiHI_nZTYbV3leIE9mBU_mRVmINBW8GhCXwiMRn70zPN4ZmrgLeJ5NNpNx1BTRUzcRo9o99u-3qFC4QD4cTvf4_v7P3-Cxk13oMxnFo2wgsF46QXNRpcSjsfAkXA1R1BN2V7lxeGC6GjI6yPycb0Sfo1YZvztT7A9pPBj2YS76gP8H1E5DOQwsZTxh2U2FwrcWGZ8JV2_wuUEra9ReqI2wxY70m61e0Gizcb48tffqsiRoli4CXbjaKpMTI1czngCb3nRdAQBs4MZPDSOHYSDQf0Y0R0e1-IYbod0TkjMgAvpbsnF8RkmvUXDe9fTM7xsEgBd8xnHV6k5ux67nXdJ-UIC63LzuGkCkxKgTwHQ1nDQpy24aoWWx2QldKrRHWVUawgPGZ5vOWhfA-OQkvO5puPydLtfUic8hYuktvJKiMqYJLUcEx4u3pt3S1I1UCE_S76CfDwVEEZaym0MrHvMEnC1YtlQyH1kHUVRY4TEiQbJ0VZR7JXOIIi8sRQcyhpRHraawoQ-_5Fn_0flOphqtv3w0yxdl8OhRRHGHpSuKUpG05Oy9OXj_zjlNYpD60RQiTLgQ50IkQRBnIaKSCkfwlYKP89iEIBVct0XXKk_RU-h9F6nc6HsGl97Ab6ZsFa5XwNIVMD4lCYsSJ1maJ9OsGiPOkqjYtqOY8WlH5kxrC9wQFC1q7Cn5R5S9TfX6KYUXSuxN6w-0GNUsXWDUsHSR8vAVNUnM0sWM_qOGn67lZMzSxWQc6dBzMo4eEj6LtGTpIqF_6spfvdRb2agj2HemyIGm-66DbIBca2_lbzT_mJPIlpx3X52jeIfX257jg87fdSXv077wLe93HPibd7q9kBzNrLueBBbeW0dORRuLvrUatGk1Rcauc4mV1Ag7WZao4dHIEtg4TNNNjlupN31nPmu8BaHkVsMYGM86b8Xn0GqaiOVGlKUFxtP45JGcF9affCfkFpTIURF9nifnoOk2XcBPfWigjcXS9RMr8KSskmfdmz987dBHC98laej6MRDH6c1rsZG0u1kdFU1Lok9XjPPgMMiNc_jY5f7Hno-C5wde70HWUgmr9n1-fXR_RDeJwXnTOCiC4-_cXY6VsXhKssEURfueAyMufft8dJY1xvMR-SQWz3_MGw2_5wc7PnD9bpynjsFYWTx_Fejfitwsnr-O3W9j8SJXGMJbPN9spC6lxcIfSTfhOYmXWixWZyKgLh3hKxOijFmm_Cx2z47J8lsSeMMG35FDZ7xvvfO1rD7o8h7wt_Kj153O5PzLYhjd39zEm-ScV0hoyNbjk6hyS7fxOQ1_qWei-wHFD8RetM6betO3jDor3_QJsXtX_FL7GYvn_FXLOH3VlGSnJuEKKTuDqdswp6IuP3ZnVvIRs9mbvJzc6ogM85zJL06utxzY2lOW-c2Bkt8QGrQ70bjjYjqonRbwsl84ky1CWMNb02534K3QrvM8LL37h3PCVV8m-MA__qErY32rhUe1hzXlqx1QUgClfseVvjdGUUNfMDhLBDuHoPb09FTweH_V33NwXTZ5WD8Sp9Pi__SgCBWIeV_rOF_TQevwJGpDDPriQwn5PjxoLD5K07p3ctsRfDIawVQHLtF9KH7YbUuLPHeqjuT7vgwgLIIofCuU2oNGpIeVsV0RZrDiPCvOFKbZH97SBRXpjkl1GdYblIH6HdZvx5lTaAmL8tsvXz5_oQShFqoytsYSWoV5Qs5jCfjsUZcOGuE8ZUwd4e_3t4uHW3BtXkuScN5uCa-xnvS2875xIfe6Y_xuK_2uzUeFqftyVv8TNdb8Dxae8btQUnKM34VSkdSFassuahZWuB3kovjmrSiwH9CDF8U3KNu6OfqmeNQlLr9bs7WiPomdRraibhllq8E6u0u6apvumuZjsRNSu-6-L11E7xQ8Qh8l8xOj481HFLnUJwqapiN8xpelDuua6H9b46XesnTVGCefadX4TMJl6Wqz2aFoNrlwOGymxccGdQnR3-BIPpGTf9MqMonHs2w6gSjqmitpnYcoEkqZp6jVXZpaQhRVtH6JnoTVUm9pNapNVGIt9FZhd9dV6CgHeT8PGVn6MRCZ0LEf1raIekfpzllFn3sHePtcYBMMcWnKUEWKn5cxfZI-5euSx_iZ2qZVNRFVXlbzYkK-oVfwQbtH1Q70-l2ldko8qfPdjp0iz7XI-E38nIiKAB1jLiFOhohnWGV4SYgFARog5i8QV8l8fFGICdAAcTpEjBMxFxeEOI8J0ADx-CXi-fiSZJzHBGiAODtDnMeTROB0djmIeZYSoAHiyQvEGY4vCzEBGiCevkCcVlV8UYgJ0ADx7CXi-Ti9LMSU3J8jnr9EnOXZZSHO8uy0eOVpMox5kzjOkkuKIBknQAPEyQvEPEmTi0JMgAaIhzEvqwReVJTOEgI0QDyIeZgin8755SBOY8IzADweAi7H-fyS3HFFeAaAsxeA4xleUFbBK8IzADwZAi4KzC4pfCDhGQCeDgDHmBSiuBzAhGYAd_YS7ji9oBlMaAZw58Mcc5qn-SXBFXMCdI6Yn0W6KuHVhE9EqGkuO8R_rT-tPv_1wLLlw955rFPOsuV_3X75dHuf8tHq_r5jTFQDtsk527SaCTGZvc323w9fb38LbLUvlRqVSgWeGZGceP4Hew_dISH0XampUmIL3nSFPDaJlXqsN622KIpdKIRP4tN2KZvE3oqmP0MjDmdmnqXvTuhIBw9fF1__eNis7-9v_7W436w_PXz98sfy6_rzp2MB6VAzOp7vKUyN_QmmY_nKOPzR0zDCylD9ch8VBrvNWFD4iCpsrZnq4x2QXzug8N7hhG438TvHEt7a2HijuP2W7qWDQrRO6i2IvmIVdv0_VkdjpfZE8ytVuPTmBwX4U5L7B0UXtHbYrDhn0O9KvN6h-EFhk6RDuddJhdr38i7bUGDuJb5YLm8fHjZ_rj_fL0jcx6LoUeZC7_0ulNhuyJS-I8yfGsf_Y9F3R1rcUZxB9lJvR6MROFOjlzW6EazJxWHtAJ1D7WUob1uhS1PD0w79DvsSd6BHB8aCNv5XTrH897_JZtaMT2sQ3mPdBPV6A40SexDWtLqriUOoc9JDNonJnqy2WLFJHLkGRThNeRCBO-5CkO0dBnsw8MY4HzXWFOhCi_PYjGANeStVd57yX4sHcHvtxTPk-7CjEyj9W3vG5MdrSS6Z-jztRDjmAyX5YhIUhhnqwLXFrm_g026DSO1BKAXOWO_IbzPO96ZlfGoRdkaVxFB6eLJGbxnnIHU4ahr2ZcDbfS-oMuwr6K0bwU3rO2_kvCTOu9MhzRxP2oavRxwsuzGEimUrxmc_Xfjvzh0yfofVtBDJmGZnIci-TdUVxCm0bVFDiIm99t4Okz5ovpLPSO7xeJD1ICkdcL4f49bwRKMlwQzPnobJ422rv4FSBRgNW1PmRvl-px8t4HOjjA0WGradZAU0qqmjyeJkv_u1RR9263qR43FsNIPCgdpX54JHV-V1Ws7TubjC62QymyfxfDKfXO2uxzGvsmqeJ5PpeDzOp-MiHedVkZaztCzLPL2S1zzmaTxNEp7Es2Q8QkxwJsZ8nIoixmrOxjHWQqoRiXNk7PYqbMNcT9JZklyFUx0unIHmXOPT4dgvZ9nqyl4HPebt1rFxrKTz7sTFS6_w-heCGrkkpcpgc6T601Ecaup3AhmfX7VWXf_6HlMY3_8FAAD__0O_Gmc">