{"id":55,"date":"2007-11-14T16:41:39","date_gmt":"2007-11-14T16:41:39","guid":{"rendered":"http:\/\/blog.danplanet.com\/wordpress\/?p=55"},"modified":"2011-11-29T16:52:50","modified_gmt":"2011-11-29T16:52:50","slug":"sblim-and-their-broken-abi","status":"publish","type":"post","link":"https:\/\/www.danplanet.com\/blog\/2007\/11\/14\/sblim-and-their-broken-abi\/","title":{"rendered":"SBLIM and their broken ABI"},"content":{"rendered":"

The CMPI standard defines the interface between a conforming provider and the CIMOM that loads it.\u00a0 It’s a massive set of data structures, types, and functions that allow the CIM server to delegate requests to providers, and for providers to make use of broker services.\u00a0 Like any standard ABI, it must be standard and uniform to allow any provider binary to be loadable in any CIMOM.<\/p>\n

Yesterday, I was debugging a strange crash that I was seeing with Pegasus<\/a> (as shipped in Fedora \"Smilie:, which was related to libcmpiutil’s asynchronous indication support.\u00a0 The indication is triggered using the CBInvokeMethod broker callback function.\u00a0 Adding debug print statements galore, I tracked it down to where the actual callback was being made.\u00a0 Since I can’t (and don’t want to) add debug print statements to Pegasus, I re-ran the whole thing in gdb.\u00a0 Sure enough, the crash is somewhere in Pegasus.\u00a0 However, I spotted something very strange in the stack trace:<\/p>\n

\n

#0\u00a0 Pegasus::value2CIMValue (data=0x2aaab285e312, type=63920, rc=0x41e00e7c)
\nat CMPI_Value.cpp:70
\n#1\u00a0 0x00002aaab16b7e2c in mbSetProperty (mb=0x5555558ab1d0,
\nctx=0x5555558ab1d0, cop=0x41e01450, name=0x555555864550 “”,
\nval=0x2aaab285e312, type=63920) at CMPI_Broker.cpp:562
\n#2\u00a0 0x00002aaab285d97d in stdi_trigger_indication ()
\nfrom \/usr\/lib64\/libcmpiutil.so.0
\n#3\u00a0 0x00002aaab18ec099 in trigger_indication (context=0x41e01450,
\nbase_type=<value optimized out>, ns=0x555555829f30 “root\/virt”\"Smilie:
\nat Virt_VirtualSystemManagementService.c:362
\n<snip><\/p>\n<\/blockquote>\n

The stdi_trigger_indication()<\/span> function is where the CBInvokeMethod()<\/span> call is made, so why is the next stack frame in the mbSetProperty()<\/span> function?\u00a0 I stewed on this a bit and then happened to notice that in cmpift.h<\/span>, setProperty<\/span> comes right after invokeMethod<\/span>.\u00a0 This was the key to the puzzle.\u00a0 Somehow, my _CMPIBrokerFT<\/span> function table was off by a void*<\/span>, which meant that I neatly executed the next function down, which was sure to fail.\u00a0 But why?<\/p>\n

I noticed that there were two cmpift.h<\/span> files on my system, one in \/usr\/include\/cmpi<\/span>, belonging to the sblim-cmpi-devel package, and another in \/usr\/include\/Pegasus\/CMPI<\/span> belonging to the tog-pegasus package.\u00a0 I thought it was a long shot, but I wrote a tiny program to print the size of the _CMPIBrokerFT<\/span> structure, and compiled it against each, and sure enough: the sblim version was 8 bytes longer!<\/p>\n

Upon further investigation, I found the problem.\u00a0 The very first parameter of _CMPIBrokerFT<\/span> was an unsigned long<\/span> in the sblim case and an unsigned int<\/span> in the Pegasus case.\u00a0 On a 32-bit platform, they are both 4-byte types, but on a 64-bit machine, the unsigned long<\/span> is 8 bytes.\u00a0 Neatly aligning the first function pointer to an 8-byte boundary meant that all my functions still “worked”, but in an off-by-one crash-you-where-you-least-expect-it kinda way.<\/p>\n

I reported it to the sblim mailing list and got a confirmation that indeed the sblim version of cmpift.h<\/span> is wrong and needs to change.\u00a0 Until then, make sure you don’t have the sblim headers on your machine when compiling 64-bit providers to be used under Pegasus or you’ll regret it!<\/p>\n","protected":false},"excerpt":{"rendered":"

The CMPI standard defines the interface between a conforming provider and the CIMOM that loads it.\u00a0 It’s a massive set of data structures, types, and functions that allow the CIM server to delegate requests to providers, and for providers to … Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[12],"tags":[28,42,41],"class_list":["post-55","post","type-post","status-publish","format-standard","hentry","category-codemonkeying","tag-cim","tag-pegasus","tag-sblim"],"yoast_head":"\nSBLIM and their broken ABI - Right Angles<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/www.danplanet.com\/blog\/2007\/11\/14\/sblim-and-their-broken-abi\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"SBLIM and their broken ABI - 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