From 40fb16a360d9c6459afee91dc793c1e3374feb94 Mon Sep 17 00:00:00 2001 From: Tom Spink Date: Thu, 5 Jun 2008 22:46:12 -0700 Subject: [PATCH] uml: deal with inaccessible address space start This patch makes os_get_task_size locate the bottom of the address space, as well as the top. This is for systems which put a lower limit on mmap addresses. It works by manually scanning pages from zero onwards until a valid page is found. Because the bottom of the address space may not be zero, it's not sufficient to assume the top of the address space is the size of the address space. The size is the difference between the top address and bottom address. [jdike@addtoit.com: changed the name to reflect that this function is supposed to return the top of the process address space, not its size and changed the return value to reflect that. Also some minor formatting changes] Signed-off-by: Tom Spink Signed-off-by: Jeff Dike Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/um/include/os.h | 2 +- arch/um/kernel/um_arch.c | 2 +- arch/um/os-Linux/sys-i386/task_size.c | 31 ++++++++++++++++++------- arch/um/os-Linux/sys-x86_64/task_size.c | 2 +- 4 files changed, 26 insertions(+), 11 deletions(-) diff --git a/arch/um/include/os.h b/arch/um/include/os.h index e2716ac888..db5be46e3e 100644 --- a/arch/um/include/os.h +++ b/arch/um/include/os.h @@ -299,6 +299,6 @@ extern int os_arch_prctl(int pid, int code, unsigned long *addr); extern int get_pty(void); /* sys-$ARCH/task_size.c */ -extern unsigned long os_get_task_size(void); +extern unsigned long os_get_top_address(void); #endif diff --git a/arch/um/kernel/um_arch.c b/arch/um/kernel/um_arch.c index 9db85b2ce6..8d84250324 100644 --- a/arch/um/kernel/um_arch.c +++ b/arch/um/kernel/um_arch.c @@ -274,7 +274,7 @@ int __init linux_main(int argc, char **argv) if (have_root == 0) add_arg(DEFAULT_COMMAND_LINE); - host_task_size = os_get_task_size(); + host_task_size = os_get_top_address(); /* * TASK_SIZE needs to be PGDIR_SIZE aligned or else exit_mmap craps * out diff --git a/arch/um/os-Linux/sys-i386/task_size.c b/arch/um/os-Linux/sys-i386/task_size.c index ccb49b0aff..be04c1e183 100644 --- a/arch/um/os-Linux/sys-i386/task_size.c +++ b/arch/um/os-Linux/sys-i386/task_size.c @@ -63,7 +63,7 @@ static int page_ok(unsigned long page) return ok; } -unsigned long os_get_task_size(void) +unsigned long os_get_top_address(void) { struct sigaction sa, old; unsigned long bottom = 0; @@ -76,9 +76,9 @@ unsigned long os_get_task_size(void) * hosts, but shouldn't hurt otherwise. */ unsigned long top = 0xffffd000 >> UM_KERN_PAGE_SHIFT; - unsigned long test; + unsigned long test, original; - printf("Locating the top of the address space ... "); + printf("Locating the bottom of the address space ... "); fflush(stdout); /* @@ -89,16 +89,31 @@ unsigned long os_get_task_size(void) sigemptyset(&sa.sa_mask); sa.sa_flags = SA_NODEFER; if (sigaction(SIGSEGV, &sa, &old)) { - perror("os_get_task_size"); + perror("os_get_top_address"); exit(1); } - if (!page_ok(bottom)) { - fprintf(stderr, "Address 0x%x no good?\n", - bottom << UM_KERN_PAGE_SHIFT); + /* Manually scan the address space, bottom-up, until we find + * the first valid page (or run out of them). + */ + for (bottom = 0; bottom < top; bottom++) { + if (page_ok(bottom)) + break; + } + + /* If we've got this far, we ran out of pages. */ + if (bottom == top) { + fprintf(stderr, "Unable to determine bottom of address " + "space.\n"); exit(1); } + printf("0x%x\n", bottom << UM_KERN_PAGE_SHIFT); + printf("Locating the top of the address space ... "); + fflush(stdout); + + original = bottom; + /* This could happen with a 4G/4G split */ if (page_ok(top)) goto out; @@ -114,7 +129,7 @@ unsigned long os_get_task_size(void) out: /* Restore the old SIGSEGV handling */ if (sigaction(SIGSEGV, &old, NULL)) { - perror("os_get_task_size"); + perror("os_get_top_address"); exit(1); } top <<= UM_KERN_PAGE_SHIFT; diff --git a/arch/um/os-Linux/sys-x86_64/task_size.c b/arch/um/os-Linux/sys-x86_64/task_size.c index fad6f57f8e..26a0dd1f34 100644 --- a/arch/um/os-Linux/sys-x86_64/task_size.c +++ b/arch/um/os-Linux/sys-x86_64/task_size.c @@ -1,4 +1,4 @@ -unsigned long os_get_task_size(unsigned long shift) +unsigned long os_get_top_address(unsigned long shift) { /* The old value of CONFIG_TOP_ADDR */ return 0x7fc0000000; -- 2.39.5