On 2014-11-18 20:34, Russell King - ARM Linux wrote:
On Tue, Nov 18, 2014 at 08:21:46PM +0400, Konstantin Khlebnikov wrote:
Usually modules are loaded into small area prior to the kernel
text because they are linked with the kernel using short calls.
Compile-time instrumentation like GCOV or KASAN bloats code a lot,
and as a result huge modules no longer fit into reserved area.
This patch adds option CONFIG_MODULES_USE_VMALLOC which lifts
limitation on amount of loaded modules. It links modules using
long-calls (option -mlong-calls) and loads them into vmalloc area.
In few places exported symbols are called from inline assembly.
This patch adds macro for such call sites: __asmbl and __asmbl_clobber.
Call turns into single 'bl' or sequence 'movw; movt; blx' depending on
context and state of config option.
Unfortunately this option isn't compatible with CONFIG_FUNCTION_TRACER.
Compiler emits short calls to profiling function despite of -mlong-calls.
This is a bug in GCC, but ftrace anyway needs an update to handle this.
It also isn't compatible with the older architectures which don't have
"blx".
Ok, I'll add "depends on CPU_V6 || CPU_V7" I don't think that it is
necessary for older cpus.
diff --git a/arch/arm/mm/mmu.c b/arch/arm/mm/mmu.c
index 9d2cdda..9e0c4f4 100644
--- a/arch/arm/mm/mmu.c
+++ b/arch/arm/mm/mmu.c
@@ -1161,16 +1161,15 @@ void __init sanity_check_meminfo(void)
static inline void prepare_page_table(void)
{
- unsigned long addr;
+ unsigned long addr = 0;
phys_addr_t end;
/*
* Clear out all the mappings below the kernel image.
*/
- for (addr = 0; addr < MODULES_VADDR; addr += PMD_SIZE)
- pmd_clear(pmd_off_k(addr));
-
#ifdef CONFIG_XIP_KERNEL
+ for ( ; addr < MODULES_VADDR; addr += PMD_SIZE)
+ pmd_clear(pmd_off_k(addr));
/* The XIP kernel is mapped in the module area -- skip over it */
addr = ((unsigned long)_etext + PMD_SIZE - 1) & PMD_MASK;
#endif
This seems to be an unrelated change. In any case, it looks wrong to
me. Please describe what you are trying to achieve here.
My patch changes MODULES_VADDR, if option enabled it becomes alias for
VMALLOC_START
It's used as border between two loops, before patch this code looks like:
/*
* Clear out all the mappings below the kernel image.
*/
for (addr = 0; addr < MODULES_VADDR; addr += PMD_SIZE)
pmd_clear(pmd_off_k(addr));
#ifdef CONFIG_XIP_KERNEL
/* The XIP kernel is mapped in the module area -- skip over it */
addr = ((unsigned long)_etext + PMD_SIZE - 1) & PMD_MASK;
#endif
for ( ; addr < PAGE_OFFSET; addr += PMD_SIZE)
pmd_clear(pmd_off_k(addr));
It's written with assumption that MODULES_VADDR < PAGE_OFFSET,
but this no longer true if modules are placed inside vmalloc area.
After patch:
unsigned long addr = 0;
/*
* Clear out all the mappings below the kernel image.
*/
#ifdef CONFIG_XIP_KERNEL
for ( ; addr < MODULES_VADDR; addr += PMD_SIZE)
pmd_clear(pmd_off_k(addr));
/* The XIP kernel is mapped in the module area -- skip over it */
addr = ((unsigned long)_etext + PMD_SIZE - 1) & PMD_MASK;
#endif
for ( ; addr < PAGE_OFFSET; addr += PMD_SIZE)
pmd_clear(pmd_off_k(addr));
Without XIP there is no reason for splitting it into two loops.
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