defines calling convention that is compatible with C calling
convention of the linux kernel on those architectures.
-Q: can multiple return values be supported in the future?
+Q: Can multiple return values be supported in the future?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A: NO. BPF allows only register R0 to be used as return value.
-Q: can more than 5 function arguments be supported in the future?
+Q: Can more than 5 function arguments be supported in the future?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A: NO. BPF calling convention only allows registers R1-R5 to be used
as arguments. BPF is not a standalone instruction set.
(unlike x64 ISA that allows msft, cdecl and other conventions)
-Q: can BPF programs access instruction pointer or return address?
+Q: Can BPF programs access instruction pointer or return address?
-----------------------------------------------------------------
A: NO.
-Q: can BPF programs access stack pointer ?
+Q: Can BPF programs access stack pointer ?
------------------------------------------
A: NO.
Only frame pointer (register R10) is accessible.
From compiler point of view it's necessary to have stack pointer.
-For example LLVM defines register R11 as stack pointer in its
+For example, LLVM defines register R11 as stack pointer in its
BPF backend, but it makes sure that generated code never uses it.
Q: Does C-calling convention diminishes possible use cases?
BPF design forces addition of major functionality in the form
of kernel helper functions and kernel objects like BPF maps with
seamless interoperability between them. It lets kernel call into
-BPF programs and programs call kernel helpers with zero overhead.
-As all of them were native C code. That is particularly the case
+BPF programs and programs call kernel helpers with zero overhead,
+as all of them were native C code. That is particularly the case
for JITed BPF programs that are indistinguishable from
native kernel C code.
------------------------------------------------------------------------
A: Soft yes.
-At least for now until BPF core has support for
+At least for now, until BPF core has support for
bpf-to-bpf calls, indirect calls, loops, global variables,
-jump tables, read only sections and all other normal constructs
+jump tables, read-only sections, and all other normal constructs
that C code can produce.
Q: Can loops be supported in a safe way?
A: This was necessary to avoid introducing flags into ISA which are
impossible to make generic and efficient across CPU architectures.
-Q: why BPF_DIV instruction doesn't map to x64 div?
+Q: Why BPF_DIV instruction doesn't map to x64 div?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A: Because if we picked one-to-one relationship to x64 it would have made
it more complicated to support on arm64 and other archs. Also it
needs div-by-zero runtime check.
-Q: why there is no BPF_SDIV for signed divide operation?
+Q: Why there is no BPF_SDIV for signed divide operation?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
A: Because it would be rarely used. llvm errors in such case and
-prints a suggestion to use unsigned divide instead
+prints a suggestion to use unsigned divide instead.
Q: Why BPF has implicit prologue and epilogue?
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~