Re: [Crash-utility] HEAD'S UP -- problem with kernels built with gcc-4.6.0

As a heads-up to those of you who are working with kernels that were compiled with the new gcc-4.6.0. I had thought that gcc-4.6.0 was painful only as far as compiling the crash utility was concerned, where there were a bunch of new "error: variable <variable> set but not used [-Werror=unused-but-set-variable] messages that I fixed in crash-5.1.2 and -5.1.3. And you may be aware that that those for-the-most-part useless warnings recently caused an LKML shitstorm w/respect to building kernels. But it's worse than that -- there is a problem with crash's embedded gdb determining the member offsets of the (large) pglist_data structure if the kernel was compiled with gcc-4.6.0. This is not specific to the gdb-7.0 version that is built into crash, but with all gdb versions as far as I can tell, certainly with gdb-7.2-48.el6 and gdb-7.2.50.20110328-31.fc15. The problem is most clearly seen with "struct -o pglist_data", which dumps the structure, showing the offset of each member. For comparison, here is the output from a (good) 2.6.38-rc4 kernel that was compiled with gcc-4.5.1: crash> help -k | grep gcc_version gcc_version: 4.5.1 crash> struct -o pglist_data struct pglist_data { [0x0] struct zone node_zones[4]; [0x1c00] struct zonelist node_zonelists[2]; [0x13e40] int nr_zones; [0x13e44] spinlock_t node_size_lock; [0x13e48] long unsigned int node_start_pfn; [0x13e50] long unsigned int node_present_pages; [0x13e58] long unsigned int node_spanned_pages; [0x13e60] int node_id; [0x13e68] wait_queue_head_t kswapd_wait; [0x13e80] struct task_struct *kswapd; [0x13e88] int kswapd_max_order; [0x13e8c] enum zone_type classzone_idx; } SIZE: 0x13f00 crash> While here is the output from a 2.6.38.2-9.fc15 kernel that was compiled with gcc-4.6.0: crash> help -k | grep gcc_version gcc_version: 4.6.0 crash> struct -o pglist_data struct pglist_data { [0x0] struct zone node_zones[4]; [0x1c00] struct zonelist node_zonelists[2]; [0x0] int nr_zones; [0x0] spinlock_t node_size_lock; [0x0] long unsigned int node_start_pfn; [0x0] long unsigned int node_present_pages; [0x0] long unsigned int node_spanned_pages; [0x0] int node_id; [0x0] wait_queue_head_t kswapd_wait; [0x0] struct task_struct *kswapd; [0x0] int kswapd_max_order; [0x0] enum zone_type classzone_idx; } SIZE: 0x13f00 crash>

I filed a bugzilla with gdb, although it may likely be a bug with the debuginfo data created by gcc-4.6.0. We'll see what happens...