Module Name: src
Committed By: uebayasi
Date: Sat Apr 12 05:25:23 UTC 2014
Modified Files:
src/sys/kern: kern_exec.c
Log Message:
execve_runproc: Unbreak __MACHINE_STACK_GROWS_UP machines. Clarify the stack
address allocation code. Summarize an awful big comment about the _rtld()
"gap".
(The log message in Rev. 1.384 was wrong; the new stack address is passed
not via the 3rd register argument, but via the SP. The 3rd is for ps_strings.)
To generate a diff of this commit:
cvs rdiff -u -r1.385 -r1.386 src/sys/kern/kern_exec.c
Please note that diffs are not public domain; they are subject to the
copyright notices on the relevant files.
Modified files:
Index: src/sys/kern/kern_exec.c
diff -u src/sys/kern/kern_exec.c:1.385 src/sys/kern/kern_exec.c:1.386
--- src/sys/kern/kern_exec.c:1.385 Fri Apr 11 18:02:33 2014
+++ src/sys/kern/kern_exec.c Sat Apr 12 05:25:23 2014
@@ -1,4 +1,4 @@
-/* $NetBSD: kern_exec.c,v 1.385 2014/04/11 18:02:33 uebayasi Exp $ */
+/* $NetBSD: kern_exec.c,v 1.386 2014/04/12 05:25:23 uebayasi Exp $ */
/*-
* Copyright (c) 2008 The NetBSD Foundation, Inc.
@@ -59,7 +59,7 @@
*/
#include <sys/cdefs.h>
-__KERNEL_RCSID(0, "$NetBSD: kern_exec.c,v 1.385 2014/04/11 18:02:33 uebayasi Exp $");
+__KERNEL_RCSID(0, "$NetBSD: kern_exec.c,v 1.386 2014/04/12 05:25:23 uebayasi Exp $");
#include "opt_exec.h"
#include "opt_execfmt.h"
@@ -243,6 +243,7 @@ struct execve_data {
int ed_szsigcode;
long ed_argc;
long ed_envc;
+ vaddr_t ed_newstack;
};
/*
@@ -778,7 +779,7 @@ execve_loadvm(struct lwp *l, const char
* Calculate the new stack size.
*/
- const size_t psstrauxlen =
+ const size_t nargenvptrs =
data->ed_argc + /* char *argv[] */
1 + /* \0 */
data->ed_envc + /* char *env[] */
@@ -804,21 +805,31 @@ execve_loadvm(struct lwp *l, const char
#endif
#ifdef __MACHINE_STACK_GROWS_UP
-/* See big comment lower down */
+/*
+ * copyargs() fills argc/argv/envp from the lower address even on
+ * __MACHINE_STACK_GROWS_UP machines. Reserve a few words just below the SP
+ * so that _rtld() use it.
+ */
#define RTLD_GAP 32
#else
#define RTLD_GAP 0
#endif
- const size_t stacklen =
+ const size_t argenvlen =
+ RTLD_GAP + /* reserved for _rtld() */
sizeof(int) + /* XXX argc in stack is long, not int */
- (psstrauxlen * ptrsz) + /* XXX auxinfo multiplied by ptr size? */
+ (nargenvptrs * ptrsz); /* XXX auxinfo multiplied by ptr size? */
+
+ const size_t sigcode_psstr_sz =
+ data->ed_szsigcode + /* sigcode */
+ data->ed_ps_strings_sz + /* ps_strings */
+ STACK_PTHREADSPACE; /* pthread space */
+
+ const size_t stacklen =
+ argenvlen +
argenvstrlen +
aslrgap +
- RTLD_GAP +
- data->ed_szsigcode +
- data->ed_ps_strings_sz +
- STACK_PTHREADSPACE;
+ sigcode_psstr_sz;
/* make the stack "safely" aligned */
const size_t aligned_stacklen = STACK_LEN_ALIGN(stacklen, STACK_ALIGNBYTES);
@@ -1117,39 +1128,36 @@ execve_runproc(struct lwp *l, struct exe
data->ed_arginfo.ps_nenvstr = data->ed_envc;
{
- char *stack;
-
- stack = (char *)STACK_ALLOC(STACK_GROW(vm->vm_minsaddr,
- STACK_PTHREADSPACE + data->ed_ps_strings_sz + data->ed_szsigcode),
- epp->ep_ssize - (data->ed_ps_strings_sz + data->ed_szsigcode));
-
-#ifdef __MACHINE_STACK_GROWS_UP
/*
- * The copyargs call always copies into lower addresses
- * first, moving towards higher addresses, starting with
- * the stack pointer that we give. When the stack grows
- * down, this puts argc/argv/envp very shallow on the
- * stack, right at the first user stack pointer.
- * When the stack grows up, the situation is reversed.
- *
- * Normally, this is no big deal. But the ld_elf.so _rtld()
- * function expects to be called with a single pointer to
- * a region that has a few words it can stash values into,
- * followed by argc/argv/envp. When the stack grows down,
- * it's easy to decrement the stack pointer a little bit to
- * allocate the space for these few words and pass the new
- * stack pointer to _rtld. When the stack grows up, however,
- * a few words before argc is part of the signal trampoline, XXX
- * so we have a problem.
+ * Allocate the stack address passed to the newly execve()'ed process.
*
- * Instead of changing how _rtld works, we take the easy way
- * out and steal 32 bytes before we call copyargs.
- * This extra space was allowed for when 'pack.ep_ssize' was calculated.
+ * The new stack address will be set to the SP (stack pointer) register
+ * in setregs().
*/
- stack += RTLD_GAP;
-#endif /* __MACHINE_STACK_GROWS_UP */
-
- /* Now copy argc, args & environ to new stack */
+
+ const size_t sigcode_psstr_sz =
+ data->ed_szsigcode + /* sigcode */
+ data->ed_ps_strings_sz + /* ps_strings */
+ STACK_PTHREADSPACE; /* pthread space */
+
+ char *stack;
+
+ /* Top of the stack address space. */
+ stack = vm->vm_minsaddr;
+
+ /* Skip pthread space, ps_strings, and sigcode. */
+ stack = STACK_GROW(stack, sigcode_psstr_sz);
+
+ /* Allocate the gap for _rtld() and arguments to be filled by copyargs(). */
+ stack = STACK_ALLOC(stack, epp->ep_ssize - sigcode_psstr_sz);
+
+ /* Skip a few words reserved for _rtld(). */
+ stack = STACK_GROW(stack, RTLD_GAP);
+
+ /* Remember the new stack address for setregs(). */
+ data->ed_newstack = (vaddr_t)stack;
+
+ /* Now copy argc, args & environ to the new stack. */
error = (*epp->ep_esch->es_copyargs)(l, epp,
&data->ed_arginfo, &stack, data->ed_argp);
@@ -1326,17 +1334,10 @@ execve_runproc(struct lwp *l, struct exe
doexechooks(p);
- {
- char * const stack = (char *)STACK_GROW(
- (void *)epp->ep_minsaddr, epp->ep_ssize);
-
/* setup new registers and do misc. setup. */
- (*epp->ep_esch->es_emul->e_setregs)(l, epp,
- (vaddr_t)stack);
+ (*epp->ep_esch->es_emul->e_setregs)(l, epp, data->ed_newstack);
if (epp->ep_esch->es_setregs)
- (*epp->ep_esch->es_setregs)(l, epp,
- (vaddr_t)stack);
- }
+ (*epp->ep_esch->es_setregs)(l, epp, data->ed_newstack);
/* Provide a consistent LWP private setting */
(void)lwp_setprivate(l, NULL);
