Filter
Top Products
Vol. 3 16-19
DEBUGGING, PROFILING BRANCHES AND TIME-STAMP COUNTER
16.4.8 LBR Stack
The last branch record stack and top-of-stack (TOS) pointer MSRs are supported
across Intel 64 and IA-32 processor families. However, the number of MSRs in the
LBR stack and the valid range of TOS pointer value can vary between different
processor families. Table 16-3 lists the LBR stack size and TOS pointer range for
several processor families according to the CPUID signatures of Display-
Family/DisplayModel encoding (see CPUID instruction in Chapter 3 of Intel® 64 and
IA-32 Architectures Software Developer’s Manual, Volume 2A).
The last branch recording mechanism tracks not only branch instructions (like JMP,
Jcc, LOOP and CALL instructions), but also other operations that cause a change in
the instruction pointer (like external interrupts, traps and faults). The branch
recording mechanisms generally employs a set of MSRs, referred to as last branch
record (LRB) stack. The size and exact locations of the LRB stack are generally
model-specific.
• Last Branch Record (LBR) Stack — The LBR consists of N pairs of MSRs (N is
listed in the LBR stack size column of Table 16-3) that store source and
destination address of recent branches (see Figure 16-3):
— MSR_LASTBRANCH_0_FROM_IP (address is model specific) through the next
consecutive (N-1) MSR address store source addresses
— MSR_LASTBRANCH_0_TO_IP (address is model specific ) through the next
consecutive (N-1) MSR address store destination addresses.
• Last Branch Record Top-of-Stack (TOS) Pointer — The lowest significant M
bits of the TOS Pointer MSR (MSR_LASTBRANCH_TOS, address is model specific)
contains an M-bit pointer to the MSR in the LBR stack that contains the most
recent branch, interrupt, or exception recorded. The valid range of the M-bit POS
pointer is given in Table 16-3.
Table 16-3. LBR Stack Size and TOS Pointer Range
DisplayFamily_DisplayModel Size of LBR Stack Range of TOS Pointer
06_1AH, 06_1EH, 06_1FH,
06_2EH
16 0 to 15
06_17H, 06_1DH 40 to 3
06_0FH 40 to 3
06_1CH 80 to 7