glibc - qsort fix

[qianxichen233]

This PR is splited from PR #164

This PR focuses on spliting out the fix for qsort function in glibc for wasm compatibility

In C, it is legal to cast a function pointer to another type (potentially with fewer parameters) and then invoke it with the “wrong” number of arguments. The qsort implementation in glibc relies on this trick. However, this behavior violates Wasm’s strict function signature rules and results in a runtime error under Wasm. More discussion here

While it’s possible to work around this with wasm-opt’s emulated function pointer casting, that approach introduces significant overhead across the entire Wasm binary. Instead, this PR directly modifies glibc’s source to remove the qsort function pointer trick, avoiding the need for binary rewriting.

The main change is duplicating the qsort implementation with a function signature that has one fewer parameter. This eliminates the function pointer casting and makes qsort work in a Wasm environment.

[rennergade]

this needs comments explaining the reasons for updates in the code, and a bit more full description here

[Yaxuan-w]

It seems moving qsort operations to entirely in user space. I noticed the reason of this listed as "wasm compatibility". I'm not sure if the reason is callback function signature mismatch. Could you make it a bit detailed?

[Yaxuan-w]

Add new line

[qianxichen233]

It seems moving qsort operations to entirely in user space. I noticed the reason of this listed as "wasm compatibility". I'm not sure if the reason is callback function signature mismatch. Could you make it a bit detailed?

See updated PR description