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Re: [PATCH][BZ #11787] Fix stack guard size accounting

On 12/12/2017 03:21 PM, Szabolcs Nagy wrote:
Previously if user requested S stack and G guard when creating a
thread, the total mapping was S and the actual available stack was
S - G - static_tls, which is not what the user requested.

This patch fixes the guard size accounting by pretending the user
requested S + G stack.  This way all later logic works out except
when reporting the user requested stack size (pthread_getattr_np)
or when computing the minimal stack size (__pthread_get_minstack).

Normally this will increase thread stack allocations by one page.
TLS accounting is not affected, that will require a separate fix.

Should this fix use a separate bug number?

2017-12-12  Szabolcs Nagy<>

	[BZ #11787]
	* nptl/allocatestack.c (allocate_stack): Add guardsize to stacksize.
	* nptl/nptl-init.c (__pthread_get_minstack): Remove guardsize from
	* nptl/pthread_getattr_np.c (pthread_getattr_np): Likewise.

Patch looks good in general. The computation for stackblock_size looks right to me.

diff --git a/nptl/allocatestack.c b/nptl/allocatestack.c
index 1cc789319564b468cf07bdb1304b27dc5a91e86f..9525322b1f92bb34aa21dcab28566aecd7434e90 100644
--- a/nptl/allocatestack.c
+++ b/nptl/allocatestack.c
@@ -532,6 +532,7 @@ allocate_stack (const struct pthread_attr *attr, struct pthread **pdp,
        /* Make sure the size of the stack is enough for the guard and
  	 eventually the thread descriptor.  */
        guardsize = (attr->guardsize + pagesize_m1) & ~pagesize_m1;
+      size += guardsize;
        if (__builtin_expect (size < ((guardsize + __static_tls_size
  				     + MINIMAL_REST_STACK + pagesize_m1)
  				    & ~pagesize_m1),

I wonder if we should add an overflow check there and return EINVAL if

  guardsize < attr->guardsize || size + guardsize < guardsize


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