[lldb-dev] Offset Calculations for Registers on Linux x86_64
Abhishek Aggarwal via lldb-dev
lldb-dev at lists.llvm.org
Fri Aug 14 00:25:47 PDT 2015
As per my understanding (please correct if I am wrong):
1. There exists a file for each platform (Architecture+OS) that calculates
the offsets for that platform. e.g. RegisterContextLinux_x86_64.cpp for
x86_64 architecture on Linux OS.
2. For each platform, offset values for registers might be different
because it depends upon the way the members of structures GPR, FPR and
UserArea are organized in Platform specific file. e.g. Offset of rax will
be 80 and not 0 for RegisterContextLinux_x86_64.cpp because rax lies at
10th position in structure GPR defined in this file.
3. The main motive behind calculating offsets for each register is to fetch
data from the correct location in a chunk of data that a ptrace API
provides (atleast in case of Linux OS).
On Thu, Aug 13, 2015 at 6:42 PM, Greg Clayton <gclayton at apple.com> wrote:
> All registers are placed into one large buffer that contains everything.
> All offsets should be the global offset in the register context's data.
> Typically we should see:
> rax offset 0
> rbx offset 8
> mm0 offset 128
> mm1 offset 160
> fpsr offset 256
> So the offsets should be based on the offset from the start of the one
> large buffer that contains all register values.
> > On Aug 13, 2015, at 2:26 AM, Abhishek Aggarwal via lldb-dev <
> lldb-dev at lists.llvm.org> wrote:
> > Hello
> > I have a question regarding offset calculations of registers for x86_64
> architecture. In file source/Plugins/Process/Utility/RegisterInfos_x86_64.h:
> > The macro FPR_OFFSET(reg) calculates the offset of floating point
> register 'reg' with respect to 'UserArea' struct while GPR_OFFSET(reg)
> calculates it wrt to 'GPR' struct. Is there any specific reason of
> calculating the offsets of floating point registers wrt 'UserArea' struct
> and not wrt 'FPR' struct (defined in
> source/Plugins/Process/Utility/RegisterContext_x86.h) ?
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