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 <Chris.Brandt@renesas.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ard Biesheuvel <redacted>
---
v2: rebased onto the split off XIP linker script
arch/arm/kernel/vmlinux-xip.lds.S | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
index 40bc4cadb959..07c642cff50e 100644
--- a/arch/arm/kernel/vmlinux-xip.lds.S
+++ b/arch/arm/kernel/vmlinux-xip.lds.S
@@ -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) {--
2.5.0
On 12 Feb 2016, Ard Biesheuvel wrote:
quoted hunk
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 <Chris.Brandt@renesas.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Ard Biesheuvel <redacted>
---
v2: rebased onto the split off XIP linker script
arch/arm/kernel/vmlinux-xip.lds.S | 1 +
1 file changed, 1 insertion(+)
diff --git a/arch/arm/kernel/vmlinux-xip.lds.S b/arch/arm/kernel/vmlinux-xip.lds.S
index 40bc4cadb959..07c642cff50e 100644
--- a/arch/arm/kernel/vmlinux-xip.lds.S
+++ b/arch/arm/kernel/vmlinux-xip.lds.S
@@ -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) {
--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
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