elfloader: arm: do not save FP and LR on stack

Since we do not have to branch to another label, there is no need to follow the ABI here. This removes 2 memory access before and after changing the state of the MMU, which should overall reduce the chance of any speculative fetches going wrong. Signed-off-by: Andy Bui <[email protected]>
seL4 · Feb 25, 2024 · 0108b77 · 0108b77
1 parent 0cdf9c2
commit 0108b77
Show file tree

Hide file tree

Showing 2 changed files with 0 additions and 10 deletions.
diff --git a/elfloader-tool/src/arch-arm/armv/armv8-a/64/mmu-hyp.S b/elfloader-tool/src/arch-arm/armv/armv8-a/64/mmu-hyp.S
@@ -53,10 +53,6 @@ clean_dcache_by_range_loop:
 END_FUNC(clean_dcache_by_range)
 
 BEGIN_FUNC(leave_hyp)
-    /* We call nested functions, follow the ABI. */
-    stp     x29, x30, [sp, #-16]!
-    mov     x29, sp
-
     /* Ensure I-cache, D-cache and mmu are disabled for EL1/Stage2 */
     mov     x9, #(1 << 31)
     msr     hcr_el2, x9
@@ -74,7 +70,6 @@ BEGIN_FUNC(leave_hyp)
     msr     spsr_el2, x9
 
     /* Let's the caller use our stack, in case it needs to pop something */
-    ldp     x29, x30, [sp], #16
     mov     x10, sp
     msr     sp_el1, x10
     msr     elr_el2, x30

diff --git a/elfloader-tool/src/arch-arm/armv/armv8-a/64/mmu.S b/elfloader-tool/src/arch-arm/armv/armv8-a/64/mmu.S
@@ -39,10 +39,6 @@ BEGIN_FUNC(flush_dcache)
 END_FUNC(flush_dcache)
 
 BEGIN_FUNC(arm_enable_mmu)
-    /* We call nested functions, follow the ABI. */
-    stp     x29, x30, [sp, #-16]!
-    mov     x29, sp
-
     /*
      *   DEVICE_nGnRnE      000     00000000
      *   DEVICE_nGnRE       001     00000100
@@ -81,6 +77,5 @@ BEGIN_FUNC(arm_enable_mmu)
     adrp    x8, arm_vector_table
     msr     vbar_el1, x8
 
-    ldp     x29, x30, [sp], #16
     ret
 END_FUNC(arm_enable_mmu)