From c62aadef3740313887ebed80277d8858fdb296ed Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Alex=20R=C3=B8nne=20Petersen?= <alex@alexrp.com>
Date: Mon, 22 Jul 2024 15:26:32 +0200
Subject: [PATCH] start: Avoid needlessly aligning the stack pointer on some
 architectures.

For these, the relevant ABIs already guarantee that it is aligned appropriately
when the kernel transfers control to _start(). Rather than potentially hiding
ABI bugs, let's actually assume that the OS works properly unless/until we have
evidence to the contrary.

This effectively reverts 81232f7c91ca8e0969e9d3f92cc11caeedc017d0.
---
 lib/std/start.zig | 21 +--------------------
 1 file changed, 1 insertion(+), 20 deletions(-)

diff --git a/lib/std/start.zig b/lib/std/start.zig
index e0f99b476248..d8486de1100f 100644
--- a/lib/std/start.zig
+++ b/lib/std/start.zig
@@ -276,13 +276,11 @@ fn _start() callconv(.Naked) noreturn {
             .x86_64 =>
             \\ xorl %%ebp, %%ebp
             \\ movq %%rsp, %%rdi
-            \\ andq $-16, %%rsp
             \\ callq %[posixCallMainAndExit:P]
             ,
             .x86 =>
             \\ xorl %%ebp, %%ebp
             \\ movl %%esp, %%eax
-            \\ andl $-16, %%esp
             \\ subl $12, %%esp
             \\ pushl %%eax
             \\ calll %[posixCallMainAndExit:P]
@@ -307,26 +305,10 @@ fn _start() callconv(.Naked) noreturn {
             \\ andi sp, sp, -16
             \\ tail %[posixCallMainAndExit]@plt
             ,
-            .mips, .mipsel =>
+            .mips, .mipsel, .mips64, .mips64el =>
             // The lr is already zeroed on entry, as specified by the ABI.
             \\ addiu $fp, $zero, 0
             \\ move $a0, $sp
-            \\ .set push
-            \\ .set noat
-            \\ addiu $1, $zero, -16
-            \\ and $sp, $sp, $1
-            \\ .set pop
-            \\ j %[posixCallMainAndExit]
-            ,
-            .mips64, .mips64el =>
-            // The lr is already zeroed on entry, as specified by the ABI.
-            \\ addiu $fp, $zero, 0
-            \\ move $a0, $sp
-            \\ .set push
-            \\ .set noat
-            \\ daddiu $1, $zero, -16
-            \\ and $sp, $sp, $1
-            \\ .set pop
             \\ j %[posixCallMainAndExit]
             ,
             .powerpc, .powerpcle =>
@@ -343,7 +325,6 @@ fn _start() callconv(.Naked) noreturn {
             \\ addis 2, 12, .TOC. - _start@ha
             \\ addi 2, 2, .TOC. - _start@l
             \\ mr 3, 1
-            \\ clrrdi 1, 1, 4
             \\ li 0, 0
             \\ stdu 0, -32(1)
             \\ mtlr 0