Re: Is the current gdb 5.1 broken for Linuxthreads?

["H . J . Lu" <hjl@lucon.org>]

On Thu, Sep 20, 2001 at 10:36:06AM +0200, Eric Paire wrote:
> 
> There is another difficulty on Linux which seems much more important than
> these ones. There is no support for MT core dumps. As Linus has always
> refused to add such functionality in the kernel (which is somewhat similar
> with your simple interface to stop all threads), a solution should be though
> of in the user space.
> 

Try the current Red Hat kernel/ac kernel. They support it. The patch is
very small. I am enclosing it here.

H.J.
--
Index: linux-2.4/fs/binfmt_aout.c
===================================================================
RCS file: /trillian/src/cvs_root/linux-2.4/fs/binfmt_aout.c,v
retrieving revision 1.1
diff -u -r1.1 binfmt_aout.c
--- linux-2.4/fs/binfmt_aout.c	2001/02/06 23:40:30	1.1
+++ linux-2.4/fs/binfmt_aout.c	2001/02/27 16:50:43
@@ -31,7 +31,8 @@
 
 static int load_aout_binary(struct linux_binprm *, struct pt_regs * regs);
 static int load_aout_library(struct file*);
-static int aout_core_dump(long signr, struct pt_regs * regs, struct file *file);
+static int aout_core_dump(long signr, struct pt_regs * regs,
+	struct file *file, struct mm_struct * mm);
 
 extern void dump_thread(struct pt_regs *, struct user *);
 
@@ -78,7 +79,8 @@
  * dumping of the process results in another error..
  */
 
-static int aout_core_dump(long signr, struct pt_regs * regs, struct file *file)
+static int aout_core_dump(long signr, struct pt_regs * regs,
+	struct file * file, struct mm_struct * mm)
 {
 	mm_segment_t fs;
 	int has_dumped = 0;
Index: linux-2.4/fs/binfmt_elf.c
===================================================================
RCS file: /trillian/src/cvs_root/linux-2.4/fs/binfmt_elf.c,v
retrieving revision 1.1
diff -u -r1.1 binfmt_elf.c
--- linux-2.4/fs/binfmt_elf.c	2001/02/06 23:40:30	1.1
+++ linux-2.4/fs/binfmt_elf.c	2001/02/27 16:50:43
@@ -56,7 +56,8 @@
  * don't even try.
  */
 #ifdef USE_ELF_CORE_DUMP
-static int elf_core_dump(long signr, struct pt_regs * regs, struct file * file);
+static int elf_core_dump(long signr, struct pt_regs * regs,
+	struct file * file, struct mm_struct * mm);
 #else
 #define elf_core_dump	NULL
 #endif
@@ -981,7 +982,8 @@
  * and then they are actually written out.  If we run out of core limit
  * we just truncate.
  */
-static int elf_core_dump(long signr, struct pt_regs * regs, struct file * file)
+static int elf_core_dump(long signr, struct pt_regs * regs,
+	struct file * file, struct mm_struct * mm)
 {
 	int has_dumped = 0;
 	mm_segment_t fs;
@@ -998,7 +1000,7 @@
 	elf_fpregset_t fpu;		/* NT_PRFPREG */
 	struct elf_prpsinfo psinfo;	/* NT_PRPSINFO */
 
-	segs = current->mm->map_count;
+	segs = mm->map_count;
 
 #ifdef DEBUG
 	printk("elf_core_dump: %d segs %lu limit\n", segs, limit);
@@ -1158,7 +1160,7 @@
 	dataoff = offset = roundup(offset, ELF_EXEC_PAGESIZE);
 
 	/* Write program headers for segments dump */
-	for(vma = current->mm->mmap; vma != NULL; vma = vma->vm_next) {
+	for(vma = mm->mmap; vma != NULL; vma = vma->vm_next) {
 		struct elf_phdr phdr;
 		size_t sz;
 
@@ -1187,7 +1189,7 @@
 
 	DUMP_SEEK(dataoff);
 
-	for(vma = current->mm->mmap; vma != NULL; vma = vma->vm_next) {
+	for(vma = mm->mmap; vma != NULL; vma = vma->vm_next) {
 		unsigned long addr;
 
 		if (!maydump(vma))
Index: linux-2.4/fs/exec.c
===================================================================
RCS file: /trillian/src/cvs_root/linux-2.4/fs/exec.c,v
retrieving revision 1.2
diff -u -r1.2 exec.c
--- linux-2.4/fs/exec.c	2001/02/07 01:17:26	1.2
+++ linux-2.4/fs/exec.c	2001/02/27 16:50:43
@@ -916,16 +916,18 @@
 
 int do_coredump(long signr, struct pt_regs * regs)
 {
+	struct mm_struct *mm;
 	struct linux_binfmt * binfmt;
-	char corename[6+sizeof(current->comm)];
+	char corename[6+sizeof(current->comm)+10];
 	struct file * file;
 	struct inode * inode;
+	int r;
 
 	lock_kernel();
 	binfmt = current->binfmt;
 	if (!binfmt || !binfmt->core_dump)
 		goto fail;
-	if (!current->dumpable || atomic_read(&current->mm->mm_users) != 1)
+	if (!current->dumpable)
 		goto fail;
 	current->dumpable = 0;
 	if (current->rlim[RLIMIT_CORE].rlim_cur < binfmt->min_coredump)
@@ -937,6 +939,8 @@
 #else
 	corename[4] = '\0';
 #endif
+ 	if (atomic_read(&current->mm->mm_users) != 1)
+ 		sprintf(&corename[4], ".%d", current->pid);
 	file = filp_open(corename, O_CREAT | 2 | O_NOFOLLOW, 0600);
 	if (IS_ERR(file))
 		goto fail;
@@ -954,10 +958,29 @@
 		goto close_fail;
 	if (do_truncate(file->f_dentry, 0) != 0)
 		goto close_fail;
-	if (!binfmt->core_dump(signr, regs, file))
-		goto close_fail;
+	/*
+	 *  Copy the mm structure to avoid potential races with
+	 *    other threads
+	 */
+	if ((mm = kmem_cache_alloc(mm_cachep, SLAB_KERNEL)) == NULL)
+		goto close_fail;
+	memcpy(mm, current->mm, sizeof(*mm));
+	if (!mm_init(mm)) {
+		kmem_cache_free(mm_cachep, mm);
+		goto close_fail;
+	}
+	down(&current->mm->mmap_sem);
+	r = dup_mmap(mm);
+	up(&current->mm->mmap_sem);
+	if (r) {
+		mmput(mm);
+		goto close_fail;
+	}
+	r = binfmt->core_dump(signr, regs, file, mm);
+	mmput(mm);
 	unlock_kernel();
-	filp_close(file, NULL);
+	if (r)
+		filp_close(file, NULL);
 	return 1;
 
 close_fail:
Index: linux-2.4/include/linux/binfmts.h
===================================================================
RCS file: /trillian/src/cvs_root/linux-2.4/include/linux/binfmts.h,v
retrieving revision 1.1
diff -u -r1.1 binfmts.h
--- linux-2.4/include/linux/binfmts.h	2001/02/06 23:41:21	1.1
+++ linux-2.4/include/linux/binfmts.h	2001/02/27 16:50:43
@@ -41,7 +41,8 @@
 	struct module *module;
 	int (*load_binary)(struct linux_binprm *, struct  pt_regs * regs);
 	int (*load_shlib)(struct file *);
-	int (*core_dump)(long signr, struct pt_regs * regs, struct file * file);
+	int (*core_dump)(long signr, struct pt_regs * regs,
+			struct file * file, struct mm_struct *mm);
 	unsigned long min_coredump;	/* minimal dump size */
 };
 
Index: linux-2.4/kernel/fork.c
===================================================================
RCS file: /trillian/src/cvs_root/linux-2.4/kernel/fork.c,v
retrieving revision 1.2
diff -u -r1.2 fork.c
--- linux-2.4/kernel/fork.c	2001/02/07 01:17:29	1.2
+++ linux-2.4/kernel/fork.c	2001/02/27 16:50:43
@@ -122,7 +122,7 @@
 	return last_pid;
 }
 
-static inline int dup_mmap(struct mm_struct * mm)
+int dup_mmap(struct mm_struct * mm)
 {
 	struct vm_area_struct * mpnt, *tmp, **pprev;
 	int retval;
@@ -197,7 +197,7 @@
 #define allocate_mm()	(kmem_cache_alloc(mm_cachep, SLAB_KERNEL))
 #define free_mm(mm)	(kmem_cache_free(mm_cachep, (mm)))
 
-static struct mm_struct * mm_init(struct mm_struct * mm)
+struct mm_struct * mm_init(struct mm_struct * mm)
 {
 	atomic_set(&mm->mm_users, 1);
 	atomic_set(&mm->mm_count, 1);