[PATCH v2 1/1] microblaze: allocate stack space for register params

[PATCH v2 1/1] microblaze: allocate stack space for register params

[Neal Frager]

C functions are invoked with arguments without allocating stack space for
register params (for potential register spills). As a result kernel built
with gcc v15 boot hangs at the point of starting init.

Add necessary stack space for few C function calls from entry.S
(not all). With this change, the kernel boots all the way to login prompt
and root login works. Simple commands like ps work and show normal
output.

Fixes: ca54502bd52a ("microblaze_mmu_v2: entry.S, entry.h")

From: Gopi Kumar Bulusu <gopi@sankhya.com>
Co-developed-by: Neal Frager <neal.frager@amd.com>
Signed-off-by: Neal Frager <neal.frager@amd.com>
---
V1->V2:
- removed whitespaces
- changed ret_from_trap2 to ret_from_trap_noadj
- added comment for SYSCALL_ARGS_SIZE
- cleaned up language in commit message
---
 arch/microblaze/kernel/entry.S | 21 +++++++++++++++------
 1 file changed, 15 insertions(+), 6 deletions(-)

diff --git a/arch/microblaze/kernel/entry.S b/arch/microblaze/kernel/entry.S
index 582d7256d815..30d42b84f156 100644
--- a/arch/microblaze/kernel/entry.S
+++ b/arch/microblaze/kernel/entry.S
@@ -339,6 +339,10 @@ C_ENTRY(mb_invalidate_icache):
  * Trap entered via brki instruction, so BIP bit is set, and interrupts
  * are masked. This is nice, means we don't have to CLI before state save
  */
+
+/* Syscall args in r5-r10 and the link register or 28 bytes */
+#define SYSCALL_ARGS_SIZE 28
+
 C_ENTRY(_user_exception):
 	swi	r1, r0, TOPHYS(PER_CPU(ENTRY_SP)) /* save stack */
 	addi	r14, r14, 4	/* return address is 4 byte after call */
@@ -422,16 +426,19 @@ C_ENTRY(_user_exception):
 	lwi	r12, r12, sys_call_table
 	/* where the trap should return need -8 to adjust for rtsd r15, 8 */
 	addi	r15, r0, ret_from_trap-8
+	addik	r1, r1, -SYSCALL_ARGS_SIZE
 	bra	r12
 
 	/* The syscall number is invalid, return an error.  */
 5:
-	braid	ret_from_trap
+	braid	ret_from_trap_noadj
 	addi	r3, r0, -ENOSYS;
 
 /* Entry point used to return from a syscall/trap */
 /* We re-enable BIP bit before state restore */
 C_ENTRY(ret_from_trap):
+	addik	r1, r1, SYSCALL_ARGS_SIZE
+C_ENTRY(ret_from_trap_noadj):
 	swi	r3, r1, PT_R3
 	swi	r4, r1, PT_R4
 
@@ -504,7 +511,7 @@ C_ENTRY(ret_from_fork):
 	bralid	r15, schedule_tail; /* ...which is schedule_tail's arg */
 	add	r5, r3, r0;	/* switch_thread returns the prev task */
 				/* ( in the delay slot ) */
-	brid	ret_from_trap;	/* Do normal trap return */
+	brid	ret_from_trap_noadj; /* Do normal trap return */
 	add	r3, r0, r0;	/* Child's fork call should return 0. */
 
 C_ENTRY(ret_from_kernel_thread):
@@ -513,13 +520,13 @@ C_ENTRY(ret_from_kernel_thread):
 				/* ( in the delay slot ) */
 	brald	r15, r20	/* fn was left in r20 */
 	addk	r5, r0, r19	/* ... and argument - in r19 */
-	brid	ret_from_trap
+	brid	ret_from_trap_noadj
 	add	r3, r0, r0
 
 C_ENTRY(sys_rt_sigreturn_wrapper):
 	addik	r30, r0, 0		/* no restarts */
 	brid	sys_rt_sigreturn	/* Do real work */
-	addik	r5, r1, 0;		/* add user context as 1st arg */
+	addik	r5, r1, SYSCALL_ARGS_SIZE;	/* add user context as 1st arg */
 
 /*
  * HW EXCEPTION rutine start
@@ -729,11 +736,13 @@ C_ENTRY(_interrupt):
 	lwi	CURRENT_TASK, r0, TOPHYS(PER_CPU(CURRENT_SAVE));
 	tovirt(r1,r1)
 	addik	r15, r0, irq_call;
+	addik	r1, r1, -SYSCALL_ARGS_SIZE
 irq_call:rtbd	r0, do_IRQ;
-	addik	r5, r1, 0;
+	addik	r5, r1, SYSCALL_ARGS_SIZE;
 
 /* MS: we are in virtual mode */
 ret_from_irq:
+	addik	r1, r1, SYSCALL_ARGS_SIZE
 	lwi	r11, r1, PT_MODE;
 	bnei	r11, 2f;
 
@@ -1302,7 +1311,7 @@ type_SYSCALL_PREEMPT:
 .global microblaze_trap_handlers
 microblaze_trap_handlers:
 	/* Exact matches come first */
-	.word ret_from_trap; .word ret_from_trap   ; .word type_SYSCALL
+	.word ret_from_trap; .word ret_from_trap_noadj  ; .word type_SYSCALL
 	.word ret_from_irq ; .word ret_from_irq    ; .word type_IRQ
 	/* Fuzzy matches go here */
 	.word ret_from_irq ; .word no_intr_resched ; .word type_IRQ_PREEMPT
-- 
2.25.1

Re: [PATCH v2 1/1] microblaze: allocate stack space for register params

[Michal Simek]

On 4/21/26 14:21, Neal Frager wrote:
> C functions are invoked with arguments without allocating stack space for
> register params (for potential register spills). As a result kernel built
> with gcc v15 boot hangs at the point of starting init.
> 
> Add necessary stack space for few C function calls from entry.S
> (not all). With this change, the kernel boots all the way to login prompt
> and root login works. Simple commands like ps work and show normal
> output.
> 
> Fixes: ca54502bd52a ("microblaze_mmu_v2: entry.S, entry.h")
> 
> From: Gopi Kumar Bulusu <gopi@sankhya.com>
> Co-developed-by: Neal Frager <neal.frager@amd.com>
> Signed-off-by: Neal Frager <neal.frager@amd.com>
> ---
> V1->V2:
> - removed whitespaces
> - changed ret_from_trap2 to ret_from_trap_noadj
> - added comment for SYSCALL_ARGS_SIZE
> - cleaned up language in commit message
> ---
>   arch/microblaze/kernel/entry.S | 21 +++++++++++++++------
>   1 file changed, 15 insertions(+), 6 deletions(-)
> 
> diff --git a/arch/microblaze/kernel/entry.S b/arch/microblaze/kernel/entry.S
> index 582d7256d815..30d42b84f156 100644
> --- a/arch/microblaze/kernel/entry.S
> +++ b/arch/microblaze/kernel/entry.S
> @@ -339,6 +339,10 @@ C_ENTRY(mb_invalidate_icache):
>    * Trap entered via brki instruction, so BIP bit is set, and interrupts
>    * are masked. This is nice, means we don't have to CLI before state save
>    */
> +
> +/* Syscall args in r5-r10 and the link register or 28 bytes */
> +#define SYSCALL_ARGS_SIZE 28
> +
>   C_ENTRY(_user_exception):
>   	swi	r1, r0, TOPHYS(PER_CPU(ENTRY_SP)) /* save stack */
>   	addi	r14, r14, 4	/* return address is 4 byte after call */
> @@ -422,16 +426,19 @@ C_ENTRY(_user_exception):
>   	lwi	r12, r12, sys_call_table
>   	/* where the trap should return need -8 to adjust for rtsd r15, 8 */
>   	addi	r15, r0, ret_from_trap-8
> +	addik	r1, r1, -SYSCALL_ARGS_SIZE
>   	bra	r12
>   
>   	/* The syscall number is invalid, return an error.  */
>   5:
> -	braid	ret_from_trap
> +	braid	ret_from_trap_noadj
>   	addi	r3, r0, -ENOSYS;
>   
>   /* Entry point used to return from a syscall/trap */
>   /* We re-enable BIP bit before state restore */
>   C_ENTRY(ret_from_trap):
> +	addik	r1, r1, SYSCALL_ARGS_SIZE
> +C_ENTRY(ret_from_trap_noadj):
>   	swi	r3, r1, PT_R3
>   	swi	r4, r1, PT_R4
>   
> @@ -504,7 +511,7 @@ C_ENTRY(ret_from_fork):
>   	bralid	r15, schedule_tail; /* ...which is schedule_tail's arg */
>   	add	r5, r3, r0;	/* switch_thread returns the prev task */
>   				/* ( in the delay slot ) */
> -	brid	ret_from_trap;	/* Do normal trap return */
> +	brid	ret_from_trap_noadj; /* Do normal trap return */
>   	add	r3, r0, r0;	/* Child's fork call should return 0. */
>   
>   C_ENTRY(ret_from_kernel_thread):
> @@ -513,13 +520,13 @@ C_ENTRY(ret_from_kernel_thread):
>   				/* ( in the delay slot ) */
>   	brald	r15, r20	/* fn was left in r20 */
>   	addk	r5, r0, r19	/* ... and argument - in r19 */
> -	brid	ret_from_trap
> +	brid	ret_from_trap_noadj
>   	add	r3, r0, r0
>   
>   C_ENTRY(sys_rt_sigreturn_wrapper):
>   	addik	r30, r0, 0		/* no restarts */
>   	brid	sys_rt_sigreturn	/* Do real work */
> -	addik	r5, r1, 0;		/* add user context as 1st arg */
> +	addik	r5, r1, SYSCALL_ARGS_SIZE;	/* add user context as 1st arg */
>   
>   /*
>    * HW EXCEPTION rutine start
> @@ -729,11 +736,13 @@ C_ENTRY(_interrupt):
>   	lwi	CURRENT_TASK, r0, TOPHYS(PER_CPU(CURRENT_SAVE));
>   	tovirt(r1,r1)
>   	addik	r15, r0, irq_call;
> +	addik	r1, r1, -SYSCALL_ARGS_SIZE
>   irq_call:rtbd	r0, do_IRQ;
> -	addik	r5, r1, 0;
> +	addik	r5, r1, SYSCALL_ARGS_SIZE;
>   
>   /* MS: we are in virtual mode */
>   ret_from_irq:
> +	addik	r1, r1, SYSCALL_ARGS_SIZE
>   	lwi	r11, r1, PT_MODE;
>   	bnei	r11, 2f;
>   
> @@ -1302,7 +1311,7 @@ type_SYSCALL_PREEMPT:
>   .global microblaze_trap_handlers
>   microblaze_trap_handlers:
>   	/* Exact matches come first */
> -	.word ret_from_trap; .word ret_from_trap   ; .word type_SYSCALL
> +	.word ret_from_trap; .word ret_from_trap_noadj  ; .word type_SYSCALL
>   	.word ret_from_irq ; .word ret_from_irq    ; .word type_IRQ
>   	/* Fuzzy matches go here */
>   	.word ret_from_irq ; .word no_intr_resched ; .word type_IRQ_PREEMPT

For a record this patch has be replaced by
https://lore.kernel.org/all/20260821151809.1233057-1-ramin.moussavi@yacoub.de/

Thanks,
Michal