ARM: vmlinux-xip.lds: assert that ROM and RAM don't overlap
PATCH v2 1/1 ARM: vmlinux-xip.lds: assert that ROM and RAM don't overlap
When building an XIP kernel, the linker produces two disjoint VMA regions, where the first is mapped onto ROM and the second onto RAM. For this reason, the linker output pointer '.' is updated halfway through the linker script, and set to a value that corresponds with the start of the RAM region.
However, in some cases, the ROM region exceeds the expected size, and the assignment of the output pointer results in a decrement rather than an increment, causing the virtual addresses of the .data region to clash with the .text region. Such a kernel cannot boot normally, but it also confuses the hell out of kallsyms, since .data symbols may appear inside the [_stext, _etext] or [_sinittext, _einittext] intervals in the first pass, but not in the second (or vice versa), resulting in inconsistent kallsyms data.
So let's make sure that the output pointer only advances, and never jumps back into the ROM region.
---
v2: rebased onto the split off XIP linker script
arch/arm/kernel/vmlinux-xip.lds.S | 1 + 1 file changed, 1 insertion(+)
arch/arm/kernel/vmlinux-xip.lds.S +1 -0
@@ -213,6 +213,7 @@ SECTIONS _exiprom = .; /* End of XIP ROM area */ __data_loc = ALIGN(4); /* location in binary */ + ASSERT(. < PAGE_OFFSET + TEXT_OFFSET, "XIP_KERNEL: ROM and RAM overlap") . = PAGE_OFFSET + TEXT_OFFSET; .data : AT(__data_loc) {
Signature · 1 line
2.5.0
PATCH v2 1/1 ARM: vmlinux-xip.lds: assert that ROM and RAM don't overlap
Quoted 41 lines · Ard Biesheuvel
When building an XIP kernel, the linker produces two disjoint VMA regions, where the first is mapped onto ROM and the second onto RAM. For this reason, the linker output pointer '.' is updated halfway through the linker script, and set to a value that corresponds with the start of the RAM region.
However, in some cases, the ROM region exceeds the expected size, and the assignment of the output pointer results in a decrement rather than an increment, causing the virtual addresses of the .data region to clash with the .text region. Such a kernel cannot boot normally, but it also confuses the hell out of kallsyms, since .data symbols may appear inside the [
_stext,_etext] or [_sinittext,_einittext] intervals in the first pass, but not in the second (or vice versa), resulting in inconsistent kallsyms data.So let's make sure that the output pointer only advances, and never jumps back into the ROM region.
Cc Chris Brandt <[email protected]>Cc Arnd Bergmann <[email protected]>Signed-off-by Ard Biesheuvel <[email protected]>---
v2: rebased onto the split off XIP linker scriptarch/arm/kernel/vmlinux-xip.lds.S | 1 + 1 file changed, 1 insertion(+)arch/arm/kernel/vmlinux-xip.lds.S +2
-1@@ -213,6 +213,7 @@ SECTIONS _exiprom = .; /* End of XIP ROM area */ __data_loc = ALIGN(4); /* location in binary */ + ASSERT(. < PAGE_OFFSET + TEXT_OFFSET, "XIP_KERNEL: ROM and RAM +overlap") . = PAGE_OFFSET + TEXT_OFFSET; .data : AT(__data_loc) { --
Quoted 1 line
2.5.0
This looks fine to me. I see no issues with it.
Of course, this is for systems with a much tighter device memory layout than what I usually use.
Chris
PATCH v2 1/1 ARM: vmlinux-xip.lds: assert that ROM and RAM don't overlap
Quoted 3 lines · On Tuesday 16 February 2016 19:18:51 Chris Brandt wrote:
This looks fine to me. I see no issues with it.
Of course, this is for systems with a much tighter device memory layout than what I usually use.
The overlap should only happen when you have really large kernel images over 16MB of readonly .text+.rodata, and I would assume this rarely happens in practice.
Arnd