On Mon, Feb 16, 2026 at 1:18 AM Thomas Munro <[email protected]> wrote: > But in this case, it seems we don't actually worry about initialising > WAL padding bytes in general. valgrind.supp has an entry to prevent > warnings about it. Should we?
Most of the xlog records are zeroed, so having different behaviour for some records feels inconsistent. For context, I've been trying to write an ImHex's pattern for WAL files[0], and stumbling upon random values was definitely confusing. On Mon, Feb 16, 2026 at 12:17 PM Bertrand Drouvot <[email protected]> wrote: > > So if I read this correctly, '{0}' will set padding bytes to 0 when > > using C11. But given Postgres is using C99, that's not something we > > can rely on? > > C11 is required as of f5e0186f865c so it looks like we could make use of > {0} instead. Ha good point, I've missed the switch to C11. So using '{0}' seems like an option. I've run some additional tests to check what was the generated machine code[1] (sorry for the long godbolt link...): - x86 clang: Calls memset - x86 gcc: Sets 128 bits + 64 bits to 0 - arm clang: Sets 64 bits * 3 to 0 - arm gcc: Sets 128 bits + 64 bits to 0 So it looks like '{0}' does zero the padding on this example. For clang, the generated machine code is the exact same as calling memset. I've found 2 other places where padding bytes aren't set: heap inplace and invalidation messages. I've updated the patch: - Initialize xl_running_xacts, xl_invalidations and xl_heap_inplace using '{0}'. - Use MemoryContextAllocZero instead of MemoryContextAlloc for shared invalidation messages [0]: https://github.com/bonnefoa/ImHex-Patterns/blob/pg_xlog/patterns/postgres_xlog.hexpat [1]: https://godbolt.org/#z:OYLghAFBqd5QCxAYwPYBMCmBRdBLAF1QCcAaPECAMzwBtMA7AQwFtMQByARg9KtQYEAysib0QXACx8BBAKoBnTAAUAHpwAMvAFYTStJg1AB9U8lIAHQ5gByrdqtrFMaYulJL6yAngGVG6ADCqLQAriwMIABMpAEAMngMtuEARpjEIJJclqgKhL4MwWER0Tl5PgIJSTap6ZnZni4VDEIETMQEReGRMY3eBa3tBFXJLGkZWR5tHV0lvdPDiaPj9QCUHqihxMjsHACkGgCCe1EAzInIYVgA1HungQoE%2BIIAdAh32AfHZxdXmLf3R7oFKoEJvD5fE7nBiXUI3O4PAjERLAcGnT5HKG/OH/BFA3xojHHI4EACeFkwWCo10exFC3mujmMdIYDBRxlUTG8CkhAHYAEJfa7XRIEYXi1TIQR3QVHYWi8XChShFKS6WnWWHYUgkKK5WqvDoYyoABu6SotFQAHcZULrqFRacosYxUlVAQABqG21y%2B2O51ikJYR4AJVCrJRXvQPq1fsETpd1wMBEwj2CLAs9BT6CjMbtDvjAcZhp5AFZBaWACJ53mVxm0ZnhtlGDlcgg8jWQo4m1DekmpgjGRKECA9w2rPmag4ATiZLObwFb3PrzmQALrewFGk31c7mNrXcOY%2Bj/ceQ4Y%2BBNhtCYnPI%2BPE/3msVc6b7M5y8cq/XtwFLzVYp3HWGikLcvqKsKLz6gBP4gWBsYQdcUEqqohrGmaxAWtaP5UGISikHaiEvG6nqGrBBHgRBLxBgOYYRkYUbkYRVHJgO6aZpg2aMUB1zbgee7HAemLdr2J6HCmZ5sCwSgEKOomPoJz4Sg287vm2Cgri4MaKlJMkQCcABsX4uKBcF5AAXpgqBUBAxnIKsE4CTuHDrLQnClrwkQcFopCoCAdkkO4BCaC56wANYgKcBkvFFsUGXFsW8tIbkcJIvAsCAvIaC807xVwvJRAAHBokilk6paFaQXk%2BX5HC8AoIAgcF3kuaQcCwEgaAZnQ6TkJQXUWD1GTIJchjAFEXBcCBNC0CmxANRAKQhaQKSJO0pKcDwK1rcQpIAPIpNoTSbbwXVsIIe0MLQG0taQWApKEwCBGItANdwvBYCwY3iLd%2BCrj4ZpvT5mCqC4oQpid5CCJgKU%2BbQeApMQ63BFgy1IngGXvaQGEgkolaYF9Rjw0YIXrBaTDAAoABqeCYFae0Ul5W38IIIhiOwUgyIIigqOot26MlY0gKYxjmPDKQNZA6yoBYzRvQAtECQHIJNvCmukyLBvA6x9M0/gXrMPTSPESw1GMdTSBYuT5AIhvRJb1vNCMZsrNIusDAsdtRG7MNNB7QzO7UExTEMXtuwsgfmxMOubNsHOue5nnLbVjKFQZ8sGZI1yjUY1wTS8XAvBo1wQLghAkLcZxcKsvDNVo6wQJ1qDdfQZAUBAA1DSgwBcKWMQzXNC1Lbdq3MLtkOj%2BtB1Hd4kNnYwBCXddy33Y9z20K9kOfd9uw%2BX9fuA8tINgxDWOijDy3i0ju0o7vtfIpjW047kmD44TwDE6ALVkwYlM03TDNGCQxZsIUQ4hOYgJ5moZaugYgGBJiLMWCNJYQGlrLAoCslanErCrLa6tiCa1TNrDwvt%2Bh%2BAgAEO22QTbVCDnoK25QChULKDbBgkcVgNFIc0QYMwQjdD0O7AQPDFi0KjgIz2fCSgNAjqbOh1cNhbB2BIBOHAPJVWTpwVO6dM7XGACNa4vcXhRBLmXIgxBK6nGrrXUmbUm4t16u3TurcQDtBYCaQq8sRrwPGpNaadBB6UGHj5Se48sYhP2odY6WN54XSujdPemAHpPRem9La28iZ3zungf6eBD63WPsgcGuwtrn1hrwK%2ByMMCZPRo/Xgz88YE2%2BiiGx5M/603pozYBsg2bgOkJApQ0D%2BZ6G8cLMw%2BhkHEJlnLTgisnjK1Vr5DChCUE6y4QUfWQRJE9EqjQ5YdQposOaF7SqDDWHsP2SBQRLQJHFG2SQrw3CZGiI4Zcm5/Ciohw6OcjIU0Y6KPjvoRO6jbop1ce4%2BWTBs7eLzoXQuxdS74DMRYqxpA66tUbigZug1W59Q7liruohiAsEzj3PufjZrpCHstcJE8doRJns1LaMTF5xJXokteKSt6NIySvbJB8iH5NBoU0%2BJToZlPGYjSpqNbo1MhvU1%2B3KP7NO/nwX%2B1N2mAKZrwEBPSOZ9NkFAvmPldCnH0ELRBEqVm%2BXQQITBczsG4LVksw0RCpb3L9uQyhWyJAxF2S7Oo3tDlMO9VwGIpynayLEYGq5wiqG9DWUIp5eyMjRreVI%2BYAdI0rG9n8uOyjAWqKTiCzRhwQwAFkdEAHFAiBAMaWIxRcTGIorlCFFaKHKkAivFF48Ve0JV7aWZKnA0rApqpweqjVUWkxUVEItY66pTu/usDCeQ/CSCAA%3D%3D%3D
v2-0001-Zero-padding-bytes-of-standby-and-heap_inplace-re.patch
Description: Binary data
