From 93dbda7cbcd70a0bd1a99f39f44a9ccde8ab9040 Mon Sep 17 00:00:00 2001 From: Jeremy Fitzhardinge Date: Thu, 26 Feb 2009 17:35:44 -0800 Subject: x86: add brk allocation for very, very early allocations Impact: new interface Add a brk()-like allocator which effectively extends the bss in order to allow very early code to do dynamic allocations. This is better than using statically allocated arrays for data in subsystems which may never get used. The space for brk allocations is in the bss ELF segment, so that the space is mapped properly by the code which maps the kernel, and so that bootloaders keep the space free rather than putting a ramdisk or something into it. The bss itself, delimited by __bss_stop, ends before the brk area (__brk_base to __brk_limit). The kernel text, data and bss is reserved up to __bss_stop. Any brk-allocated data is reserved separately just before the kernel pagetable is built, as that code allocates from unreserved spaces in the e820 map, potentially allocating from any unused brk memory. Ultimately any unused memory in the brk area is used in the general kernel memory pool. Initially the brk space is set to 1MB, which is probably much larger than any user needs (the largest current user is i386 head_32.S's code to build the pagetables to map the kernel, which can get fairly large with a big kernel image and no PSE support). So long as the system has sufficient memory for the bootloader to reserve the kernel+1MB brk, there are no bad effects resulting from an over-large brk. Signed-off-by: Jeremy Fitzhardinge Signed-off-by: H. Peter Anvin --- arch/x86/include/asm/sections.h | 7 +++++++ arch/x86/include/asm/setup.h | 4 ++++ 2 files changed, 11 insertions(+) (limited to 'arch/x86/include') diff --git a/arch/x86/include/asm/sections.h b/arch/x86/include/asm/sections.h index 2b8c5160388..1b7ee5d673c 100644 --- a/arch/x86/include/asm/sections.h +++ b/arch/x86/include/asm/sections.h @@ -1 +1,8 @@ +#ifndef _ASM_X86_SECTIONS_H +#define _ASM_X86_SECTIONS_H + #include + +extern char __brk_base[], __brk_limit[]; + +#endif /* _ASM_X86_SECTIONS_H */ diff --git a/arch/x86/include/asm/setup.h b/arch/x86/include/asm/setup.h index 05c6f6b11fd..45454f3fa12 100644 --- a/arch/x86/include/asm/setup.h +++ b/arch/x86/include/asm/setup.h @@ -100,6 +100,10 @@ extern struct boot_params boot_params; */ #define LOWMEMSIZE() (0x9f000) +/* exceedingly early brk-like allocator */ +extern unsigned long _brk_end; +void *extend_brk(size_t size, size_t align); + #ifdef __i386__ void __init i386_start_kernel(void); -- cgit v1.2.3