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Date: Fri, 14 Nov 2014 14:10:02 -0800 From: Jay Vosburgh <jay.vosburgh@...onical.com> To: Hannes Frederic Sowa <hannes@...essinduktion.org> cc: David Miller <davem@...emloft.net>, eric.dumazet@...il.com, netdev@...r.kernel.org, ogerlitz@...lanox.com, pshelar@...ira.com, jesse@...ira.com, discuss@...nvswitch.org Subject: Re: [PATCH net-next] fast_hash: clobber registers correctly for inline function use Hannes Frederic Sowa <hannes@...essinduktion.org> wrote: [...] >I created it via the function calling convention documented in >arch/x86/include/asm/calling.h, so I specified each register which a >function is allowed to clobber with. > >I currently cannot see how I can resolve the invalid constraints error >easily. :( > >So either go with my first patch, which I puts the alternative_call >switch point into its own function without ever inlining or the patch >needs to be reverted. :/ As a data point, I tested the first patch as well, and the system does not panic with it in place. Inspection shows that it's using %r14 in place of %r8 in the prior (crashing) implementation. Disassembly of the call site (on the non-sse4_1 system) in ovs_flow_tbl_insert with the first patch applied looks like this: 0xffffffffa00b6bb9 <ovs_flow_tbl_insert+0xb9>: mov %r15,0x348(%r14) 0xffffffffa00b6bc0 <ovs_flow_tbl_insert+0xc0>: movzwl 0x28(%r15),%ecx 0xffffffffa00b6bc5 <ovs_flow_tbl_insert+0xc5>: movzwl 0x2a(%r15),%esi 0xffffffffa00b6bca <ovs_flow_tbl_insert+0xca>: movzwl %cx,%eax 0xffffffffa00b6bcd <ovs_flow_tbl_insert+0xcd>: sub %ecx,%esi 0xffffffffa00b6bcf <ovs_flow_tbl_insert+0xcf>: lea 0x38(%r14,%rax,1),%rdi 0xffffffffa00b6bd4 <ovs_flow_tbl_insert+0xd4>: sar $0x2,%esi 0xffffffffa00b6bd7 <ovs_flow_tbl_insert+0xd7>: callq 0xffffffff813a7810 <__jhash2> 0xffffffffa00b6bdc <ovs_flow_tbl_insert+0xdc>: mov %eax,0x30(%r14) 0xffffffffa00b6be0 <ovs_flow_tbl_insert+0xe0>: mov (%rbx),%r13 0xffffffffa00b6be3 <ovs_flow_tbl_insert+0xe3>: mov %r14,%rsi 0xffffffffa00b6be6 <ovs_flow_tbl_insert+0xe6>: mov %r13,%rdi 0xffffffffa00b6be9 <ovs_flow_tbl_insert+0xe9>: callq 0xffffffffa00b61a0 <table_instance_insert> Compared to the panicking version's function: 0xffffffffa01a55c9 <ovs_flow_tbl_insert+0xb9>: mov %r15,0x348(%r8) 0xffffffffa01a55d0 <ovs_flow_tbl_insert+0xc0>: movzwl 0x28(%r15),%ecx 0xffffffffa01a55d5 <ovs_flow_tbl_insert+0xc5>: movzwl 0x2a(%r15),%esi 0xffffffffa01a55da <ovs_flow_tbl_insert+0xca>: movzwl %cx,%eax 0xffffffffa01a55dd <ovs_flow_tbl_insert+0xcd>: sub %ecx,%esi 0xffffffffa01a55df <ovs_flow_tbl_insert+0xcf>: lea 0x38(%r8,%rax,1),%rdi 0xffffffffa01a55e4 <ovs_flow_tbl_insert+0xd4>: sar $0x2,%esi 0xffffffffa01a55e7 <ovs_flow_tbl_insert+0xd7>: callq 0xffffffff813a75c0 <__jhash2> 0xffffffffa01a55ec <ovs_flow_tbl_insert+0xdc>: mov %eax,0x30(%r8) 0xffffffffa01a55f0 <ovs_flow_tbl_insert+0xe0>: mov (%rbx),%r13 0xffffffffa01a55f3 <ovs_flow_tbl_insert+0xe3>: mov %r8,%rsi 0xffffffffa01a55f6 <ovs_flow_tbl_insert+0xe6>: mov %r13,%rdi 0xffffffffa01a55f9 <ovs_flow_tbl_insert+0xe9>: callq 0xffffffffa01a4ba0 <table_instance_insert> It appears to generate the same instructions, but allocates registers differently (using %r14 instead of %r8). The __jhash2 disassembly appears to be unchanged between the two versions. -J --- -Jay Vosburgh, jay.vosburgh@...onical.com -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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