[lldb-dev] 32-bit linux IsWatchpointHit assertion failure due to WriteRegister

Matthew Gardiner mg11 at csr.com
Mon Mar 3 06:02:31 PST 2014

Yes, my latest pain in 32-bit linux occurs due to the offset calculations for dr6/7 being broken by the inclusion of the extended floating point registers structure in "struct UserArea". I'm not 
really sure what we are trying to model here, since, looking at sys/user.h, it's the regular FP registers (user_fpregs_struct) which comprise the user area not the extended ones (user_fpxregs_struct).

I did try to fix this issue by reinstating the previous definition for FPR_i386, i.e.

struct FPR_i386
     int32_t cwd;
     int32_t swd;
     int32_t twd;
     int32_t fip;
     int32_t fcs;
     int32_t foo;
     int32_t fos;
     int32_t st_space [20];

Unfortunately, this results in a world of pain, since the numerous "DEFINE_FPR" invocations in RegisterInfos_i386.h rely on the elements contained in user_fpxregs_struct.

So, I solved this issue in a different (and in my opinion simpler) way - by using the following macro to calculate the offset of a debug register in the user:

#define DR_OFFSET(reg_index) \
     (0xFC + (reg_index * 4))

Can't we just use this in our lldb code?

Why do we currently calculate the offsets with copied structures? Do we actually use the structures as structures as well? This is a source of bugs.

So I'll repeat what I hint to above...

Can we remove the copied user/register structures and replace the required offsets with integral constant definitions please?

Matthew Gardiner

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