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For a toy application on x86_64, for example, following is the SFrame stack trace information for the 3 pltN entries of 16 bytes each: func idx [1]: pc = 0x401030, size = 48 bytes STARTPC[m] CFA FP RA 0000000000000000 sp+8 u u 000000000000000b sp+16 u u The data in first column is the start_ip_offset. Also note that the FDE is of type SFRAME_FDE_TYPE_PCMASK (denoted by the [m] on LHS). Where each pltN (note: excluding plt0 entry) entry looks like: 401030: jmp *0x2fca(%rip) 401036: push $0x0 40103b: jmp 401020<_init+0x20> 401040: jmp *0x2fc2(%rip) 401046: push $0x1 40104b: jmp 401020<_init+0x20> 401050: jmp *0x2fba(%rip) 401056: push $0x2 40105b: jmp 401020<_init+0x20> Now, to find SFrame stack trace information from an FDE of type SFRAME_FDE_TYPE_PCMASK, sframe_find_fre () was doing an operation like, (start_ip_offset & 0xf) >= (pc & 0xf) This works for pltN entry of size, say, less than 16 bytes. But if the pltN entries or similar code stubs (for which SFrame FDE of type SFRAME_FDE_TYPE_PCMASK may be used), evolve to be of size > 16 bytes, this will cease to work. To match the range covered by the SFrame FRE, one should instead perform a modulo operation. The constant for the modulo operation must be the size of the pltN entry. Further, this constant should ideally be encoded in the format, as it may be different for each ABI. In SFrame Version 2 of the format, we will move towards encoding it explicitly in the SFrame FDE. For now, fix up the logic to at least move towards modulo operation. libsframe/ * sframe.c (sframe_fre_check_range_p): New definition. (sframe_find_fre): Refactor a bit and use the new definition above. include/ * sframe.h (SFRAME_FDE_TYPE_PCMASK): Update comment. libsframe/doc/ * sframe-spec.texi: Fix the text for SFRAME_FDE_TYPE_PCMASK FDE type.
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