| Message ID | 1273756645-11149-1-git-send-email-Martin.Jansa@gmail.com |
|---|---|
| State | New |
| Headers | show |
On 05/13/2010 06:17 AM, Martin Jansa wrote: > @@ -2899,8 +2900,14 @@ int main(int argc, char **argv, char **envp) > if (fscanf(fp, "%lu", &tmp) == 1) { > mmap_min_addr = tmp; > qemu_log("host mmap_min_addr=0x%lx\n", mmap_min_addr); > + } else { > + qemu_log("cannot read value from /proc/sys/vm/mmap_min_addr, assuming %d\n", MMAP_MIN_ADDR_DEFAULT); > + mmap_min_addr = MMAP_MIN_ADDR_DEFAULT; > } > fclose(fp); > + } else { > + qemu_log("cannot open /proc/sys/vm/mmap_min_addr for reading, assuming %d\n", MMAP_MIN_ADDR_DEFAULT); > + mmap_min_addr = MMAP_MIN_ADDR_DEFAULT; > } > } Perhaps you can combine these two else clauses? r~
On Thu, May 13, 2010 at 09:59:24AM -0700, Richard Henderson wrote: > On 05/13/2010 06:17 AM, Martin Jansa wrote: > > @@ -2899,8 +2900,14 @@ int main(int argc, char **argv, char **envp) > > if (fscanf(fp, "%lu", &tmp) == 1) { > > mmap_min_addr = tmp; > > qemu_log("host mmap_min_addr=0x%lx\n", mmap_min_addr); > > + } else { > > + qemu_log("cannot read value from /proc/sys/vm/mmap_min_addr, assuming %d\n", MMAP_MIN_ADDR_DEFAULT); > > + mmap_min_addr = MMAP_MIN_ADDR_DEFAULT; > > } > > fclose(fp); > > + } else { > > + qemu_log("cannot open /proc/sys/vm/mmap_min_addr for reading, assuming %d\n", MMAP_MIN_ADDR_DEFAULT); > > + mmap_min_addr = MMAP_MIN_ADDR_DEFAULT; > > } > > } > > Perhaps you can combine these two else clauses? Sure it would be possible, but while trying to find why qemu doesn't work on someone box but works on mine I wanted to distinguish between cannot open and cannot read. Also if I combine it in test ie initialize mmap_min_addr with -1, and then check if it changed after read (because 0 is also valid value), or moving fopen and fscanf to one condition, then it gets IMHO as complicated as those 2 else clauses. BTW: I noticed that qemu-arm works ok when mmap_min_addr is low enough (and doesn't have to be zero). my box had mmap_min_addr 4096 and qemu-arm worked fine even without reading it and the other boxes had mmap_min_addr = 64K and failed later to mmap. Regards,
On 05/13/2010 12:26 PM, Martin Jansa wrote: > BTW: I noticed that qemu-arm works ok when mmap_min_addr is low enough > (and doesn't have to be zero). > > my box had mmap_min_addr 4096 and qemu-arm worked fine even without > reading it Paul Brook's c581deda322080e8beb88b2e468d4af54454e4b3 had the side effect of working around mmap_min_addr without having to read it. Of course, if we *can* read mmap_min_addr, his patch will do less work. r~
diff --git a/linux-user/main.c b/linux-user/main.c index 18b52c0..94b6465 100644 --- a/linux-user/main.c +++ b/linux-user/main.c @@ -2891,6 +2891,7 @@ int main(int argc, char **argv, char **envp) * When loading the ELF image to determine whether guest_base * is needed. It is also used in mmap_find_vma. */ +#define MMAP_MIN_ADDR_DEFAULT 65536 { FILE *fp; @@ -2899,8 +2900,14 @@ int main(int argc, char **argv, char **envp) if (fscanf(fp, "%lu", &tmp) == 1) { mmap_min_addr = tmp; qemu_log("host mmap_min_addr=0x%lx\n", mmap_min_addr); + } else { + qemu_log("cannot read value from /proc/sys/vm/mmap_min_addr, assuming %d\n", MMAP_MIN_ADDR_DEFAULT); + mmap_min_addr = MMAP_MIN_ADDR_DEFAULT; } fclose(fp); + } else { + qemu_log("cannot open /proc/sys/vm/mmap_min_addr for reading, assuming %d\n", MMAP_MIN_ADDR_DEFAULT); + mmap_min_addr = MMAP_MIN_ADDR_DEFAULT; } }
* 65536 is default at least for ubuntu and fedora. * after http://git.kernel.org/?p=linux/kernel/git/torvalds/linux-2.6.git;a=commit;h=0e1a6ef2dea88101b056b6d9984f3325c5efced3 it's not readable by normal user on many systems * there is patch to enable read-only access again http://git.kernel.org/?p=linux/kernel/git/jmorris/security-testing-2.6.git;a=commitdiff;h=822cceec7248013821d655545ea45d1c6a9d15b3 but that's not applied in many distributions * please consider this workaround Signed-off-by: Martin Jansa <Martin.Jansa@gmail.com> --- linux-user/main.c | 7 +++++++ 1 files changed, 7 insertions(+), 0 deletions(-)