From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Eli Zaretskii" To: dmj+@andrew.cmu.edu Cc: gdb-patches@sources.redhat.com Subject: Re: [RFA] mips: Fix "info registers" output Date: Thu, 21 Jun 2001 12:00:00 -0000 Message-id: <1438-Thu21Jun2001215717+0300-eliz@is.elta.co.il> References: <20010621083624.A9719@nevyn.them.org> <20010621094418.A30641@nevyn.them.org> X-SW-Source: 2001-06/msg00367.html > Date: Thu, 21 Jun 2001 09:44:18 -0700 > From: Daniel Jacobowitz > > Aha! Let me guess - Irix 6.5 is using the FP registers in 8 byte mode, > right? Yes. > There was indeed a bug on that path of the code, but it doesn't > actually affect the output. We have this: > > raw_buffer[0] = (char *) alloca (REGISTER_RAW_SIZE (FP0_REGNUM)); > raw_buffer[1] = (char *) alloca (REGISTER_RAW_SIZE (FP0_REGNUM)); > dbl_buffer = (char *) alloca (2 * REGISTER_RAW_SIZE (FP0_REGNUM)); > > /* Get the data in raw format. */ > if (read_relative_register_raw_bytes (regnum, raw_buffer[HI])) > error ("can't read register %d (%s)", regnum, REGISTER_NAME (regnum)); > > [snip] > > memcpy (dbl_buffer, raw_buffer[HI], 2 * REGISTER_RAW_SIZE (FP0_REGNUM)); > flt1 = unpack_double (builtin_type_float, > &raw_buffer[HI][offset], &inv1); > doub = unpack_double (builtin_type_double, dbl_buffer, &inv3); > > So we're copying 2 * 8 bytes out of an 8 byte buffer. I don't think so. The memcpy part uses raw_buffer[HI] as its address, but the two buffers whose addresses are in raw_buffer[0] and raw_buffer[1] are layed out on the stack one after the other. So you have enough space there, and memcpy can copy up to 2*8 bytes without fear. It's nasty code, but it works. (No, I didn't write that code ;-) > The real killer is on the other branch, size == 4: > memcpy (dbl_buffer, raw_buffer, 2 * REGISTER_RAW_SIZE (FP0_REGNUM)); > > raw_buffer points to 8 bytes, sure enough - but they're both pointers > to four byte buffers before my patch. That won't decode. So why replacing raw_buffer with raw_buffer[HI] in the call to memcpy isn't all that is needed to fix this?