path: root/arch/arm/kernel/head-common.S
diff options
authorNicolas Pitre <>2017-08-25 00:54:18 -0400
committerNicolas Pitre <>2017-09-10 19:34:53 -0400
commitca8b5d97d6bfd2d24cec053bbbe35cf356bec4e3 (patch)
tree36950a2d9a13a56761d182771ebcd795fb17c798 /arch/arm/kernel/head-common.S
parent0d302c710bf04149b6de7cd9a7064d0ca6cd4bea (diff)
ARM: XIP kernel: store .data compressed in ROMxip_zdata
The .data segment stored in ROM is only copied to RAM once at boot time and never referenced afterwards. This is arguably a suboptimal usage of ROM resources. This patch allows for compressing the .data segment before storing it into ROM and decompressing it to RAM rather than simply copying it, saving on precious ROM space. Because global data is not available yet (obviously) we must allocate decompressor workspace memory on the stack. The .bss area is used as a stack area for that purpose before it is cleared. The required stack frame is 9568 bytes for __inflate_kernel_data() alone, so make sure the .bss is large enough to cope with that plus extra room for called functions or fail the build. Those numbers were picked arbitrarily based on the above 9568 byte stack frame: 10240 (2.5 * PAGE_SIZE): used to override -Wframe-larger-than whose default value is 1024. 12288 (3 * PAGE_SIZE): minimum .bss size to contain the stack. Signed-off-by: Nicolas Pitre <> Reviewed-by: Ard Biesheuvel <> Tested-by: Chris Brandt <>
Diffstat (limited to 'arch/arm/kernel/head-common.S')
1 files changed, 10 insertions, 1 deletions
diff --git a/arch/arm/kernel/head-common.S b/arch/arm/kernel/head-common.S
index bf9c4e38eced..a25027b87a60 100644
--- a/arch/arm/kernel/head-common.S
+++ b/arch/arm/kernel/head-common.S
@@ -87,7 +87,14 @@ __mmap_switched:
adr r4, __mmap_switched_data
mov fp, #0
+ ARM( ldr sp, [r4], #4 )
+ THUMB( ldr sp, [r4] )
+ THUMB( add r4, #4 )
+ bl __inflate_kernel_data @ decompress .data to RAM
+ teq r0, #0
+ bne __error
+#elif defined(CONFIG_XIP_KERNEL)
ARM( ldmia r4!, {r0, r1, r2, sp} )
THUMB( ldmia r4!, {r0, r1, r2, r3} )
THUMB( mov sp, r3 )
@@ -114,9 +121,11 @@ ENDPROC(__mmap_switched)
.type __mmap_switched_data, %object
.long _sdata @ r0
.long __data_loc @ r1
.long _edata_loc @ r2
.long __bss_stop @ sp (temporary stack in .bss)