Thanks :)
>
> Changes since v1:
> https://lore.kernel.org/linux-um/20241017231007.1500497-2-david...@google.com/
> - Use force_arg_align_pointer on real_init() instead of naked on
> __start, which works with clang.
I already applied it, so need to fix on top of it now, not replace it.
However I was just playing with the below - was just looking at the size
though, but what do you think?
johannes
>From 57c5a80a4db2de33a11a5a20fcbea8f3643844f5 Mon Sep 17 00:00:00 2001
From: Johannes Berg <johannes.b...@intel.com>
Date: Tue, 22 Oct 2024 11:48:21 +0200
Subject: [PATCH] um: make stub_exe _start() pure inline asm
Since __attribute__((naked)) cannot be used with functions
containing C statements, just generate the few instructions
it needs in assembly directly.
Fixes: 8508a5e0e9db ("um: Fix misaligned stack in stub_exe")
Link:
https://lore.kernel.org/linux-um/cabvgosnth-uoofmp5hwmxjx_f1osmnvdhgkrkm4uz6dfm2l...@mail.gmail.com/
Signed-off-by: Johannes Berg <johannes.b...@intel.com>
---
arch/um/kernel/skas/stub_exe.c | 8 +-------
arch/x86/um/shared/sysdep/stub_32.h | 8 ++++++++
arch/x86/um/shared/sysdep/stub_64.h | 8 ++++++++
3 files changed, 17 insertions(+), 7 deletions(-)
diff --git a/arch/um/kernel/skas/stub_exe.c b/arch/um/kernel/skas/stub_exe.c
index 722ce6267476..a61f9c008233 100644
--- a/arch/um/kernel/skas/stub_exe.c
+++ b/arch/um/kernel/skas/stub_exe.c
@@ -81,11 +81,5 @@ noinline static void real_init(void)
__attribute__((naked)) void _start(void)
{
- char *alloc;
-
- /* Make enough space for the stub (including space for alignment) */
- alloc = __builtin_alloca((1 + 2 * STUB_DATA_PAGES - 1) *
UM_KERN_PAGE_SIZE);
- asm volatile("" : "+r,m"(alloc) : : "memory");
-
- real_init();
+ stub_start(real_init);
}
diff --git a/arch/x86/um/shared/sysdep/stub_32.h
b/arch/x86/um/shared/sysdep/stub_32.h
index 631a18d0ff44..760e8ce8093f 100644
--- a/arch/x86/um/shared/sysdep/stub_32.h
+++ b/arch/x86/um/shared/sysdep/stub_32.h
@@ -123,4 +123,12 @@ static __always_inline void *get_stub_data(void)
return (void *)ret;
}
+
+#define stub_start(fn) \
+ asm volatile ( \
+ "subl %0,%%esp ;" \
+ "movl %1, %%eax ; " \
+ "call *%%eax ;" \
+ :: "i" ((STUB_DATA_PAGES + 1) * UM_KERN_PAGE_SIZE), \
+ "i" (&fn))
#endif
diff --git a/arch/x86/um/shared/sysdep/stub_64.h
b/arch/x86/um/shared/sysdep/stub_64.h
index 17153dfd780a..148bf423289e 100644
--- a/arch/x86/um/shared/sysdep/stub_64.h
+++ b/arch/x86/um/shared/sysdep/stub_64.h
@@ -126,4 +126,12 @@ static __always_inline void *get_stub_data(void)
return (void *)ret;
}
+
+#define stub_start(fn) \
+ asm volatile ( \
+ "subq %0,%%rsp ;" \
+ "movq %1,%%rax ;" \
+ "call *%%rax ;" \
+ :: "i" ((STUB_DATA_PAGES + 1) * UM_KERN_PAGE_SIZE), \
+ "i" (&fn))
#endif
--
2.47.0
